How Bitcoin Custody Works: What Every Heir Needs to Know

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The most common mistake heirs make with Bitcoin isn't selling at the wrong time or moving funds to the wrong place. It's misunderstanding how custody works. They assume it's like a bank account. It isn't. Before you touch anything, you need to understand who is holding what, where, and why that changes everything about how you handle this inheritance.

This article explains the major custody arrangements you might encounter, what each one means for you as an heir, and — critically — what you must never do, regardless of how urgent it feels or how trustworthy the person asking seems.

The Foundational Concept: "Not Your Keys, Not Your Coins"

This phrase — repeated often in Bitcoin circles — is not a slogan. It is a factual description of how Bitcoin works. On the Bitcoin network, ownership is controlled entirely by private keys. A private key is a secret number that authorizes transactions. Whoever holds the key can move the Bitcoin. Whoever doesn't, can't.

When someone holds their own private keys — typically through a hardware wallet — they are in complete, direct control of their Bitcoin. No third party can freeze the account, reverse a transaction, or deny access. The Bitcoin responds only to the key.

When someone leaves their Bitcoin on an exchange — a platform like Coinbase, Kraken, or Gemini — they do not hold their own keys. The exchange holds the keys on their behalf. This is custodial Bitcoin, and it works more like a brokerage account: the platform controls the underlying asset, and you have a claim against them.

These two arrangements require completely different approaches to inheritance. Your first task as an heir is to determine which one you're dealing with — and that starts with the documentation your family member left behind.

The Four Major Custody Arrangements

Before diving into specifics, it helps to map the landscape. Bitcoin custody falls into four broad categories, each with distinct inheritance implications:

Your family member may have used one arrangement or a combination. More sophisticated holders often segment their Bitcoin: keep a smaller amount on an exchange for liquidity, hold the bulk in self-custody, and structure the largest positions in multisig. The documentation they left behind — a Letter of Instruction, a will attachment, a sealed envelope — should specify which approach they used and where to find the relevant credentials.

For a complete overview of custody architectures and how they interact with estate planning, see our guide to Bitcoin custody solutions for family offices.

Hardware Wallets: What They Are and What to Do With Them

A hardware wallet is a small physical device — often resembling a USB drive or a calculator — that stores private keys offline. The most common brands are Coldcard, Ledger, and Trezor. These devices are specifically designed so that the private keys never leave the hardware and are never exposed to the internet.

When you find a hardware wallet among a deceased person's belongings, treat it with the same care you would treat physical gold or an original deed. It is the access point to the Bitcoin. It should be:

• Stored in a secure location immediately — a safe, a lockbox, or another physically protected space
• Not plugged into any computer until you have legal guidance
• Not shown to or handled by anyone who isn't directly involved in the estate
• Documented — note where you found it, its condition, and any visible markings

Hardware wallets are typically protected by a PIN. Without the PIN, the device will lock after a number of failed attempts (usually 3–10 depending on the device). But even if the device is locked or lost, the Bitcoin can be recovered — if and only if the seed phrase is available.

Common Hardware Wallet Models You May Encounter

Each device looks slightly different and has a different form factor, but they all serve the same purpose:

• Coldcard: A rectangular device with a number pad and small screen. Often used by technically sophisticated holders. Has an advanced security chip and supports air-gapped operation (no USB required).
• Ledger Nano S/X: One of the most widely-used consumer hardware wallets. Small device, connects via USB or Bluetooth (on the X model). Uses a 24-word seed phrase.
• Trezor Model One/T: Early and popular hardware wallets with a small screen and physical confirmation buttons. Uses either 12 or 24-word seed phrases.
• Foundation Passport: Open-source hardware wallet with a larger screen and battery. Designed for air-gapped operation.

Do not attempt to interact with the device — plugging it in, entering PINs, or connecting it to software — without professional guidance. The goal at this stage is inventory and preservation, not access.

Seed Phrases: The Master Key

The seed phrase — sometimes called a recovery phrase or mnemonic — is a sequence of 12 or 24 common English words, usually written on paper or stamped into a metal plate. It is the most important item in any Bitcoin estate. It is the master key from which all private keys in the wallet are derived.

If someone has the seed phrase, they can regenerate the entire wallet on a new device and access every address that wallet ever controlled. This is both the strength and the danger of seed phrases. They make recovery possible. They also make theft devastatingly simple.

Where Seed Phrases Are Typically Stored

Sophisticated Bitcoin holders store their seed phrases away from the device itself, specifically so that the two access factors — device + seed — are never in the same location. Common storage locations include:

• Metal plates or tiles: Steel or titanium plates with the words stamped or engraved. Fireproof and waterproof. Often stored in a safe or safety deposit box.
• Paper in a sealed envelope: Basic but effective if stored securely. Vulnerable to fire and water.
• Home safes: Fireproof safes are a common storage point for both the device and the seed phrase — though security-conscious holders keep them separated.
• Attorney's office or safety deposit box: Third-party storage for redundancy, often with instructions in the will or estate documents.
• Encrypted digital storage: Some holders encrypt and store seed phrases digitally, though this is generally considered inferior to physical storage by most security practitioners.

If you find a seed phrase — on paper, in a notebook, stamped in metal, stored in a safe — do not:

• Photograph it and store the photo in a cloud account
• Type it into any website, app, or form — no matter how legitimate it appears
• Read it aloud on a phone call or video call
• Share it with anyone outside of a physically secure, legally supervised process
• Store it digitally in any form you do not fully control

Any website or person that asks you to enter a seed phrase online is attempting to steal the Bitcoin. Legitimate Bitcoin professionals — advisers, attorneys, even hardware wallet manufacturers — have no reason to ask for your seed phrase. Ever.

The 25th Word: Passphrases and Advanced Security

Some Bitcoin holders add an additional layer of security on top of the standard 24-word seed phrase: a passphrase, sometimes called the "25th word." Unlike the seed words (which come from a fixed list of 2,048 English words), a passphrase can be any string of characters — a word, a phrase, a combination of numbers and symbols.

The passphrase modifies the wallet in a mathematically predictable way. A seed phrase with a passphrase produces a completely different set of addresses than the same seed phrase without one. An attacker who finds your seed phrase but doesn't know the passphrase cannot access those funds — they'll see an empty wallet.

Passphrases, when used, are often stored separately from the seed phrase — sometimes in a different physical location, with a different trusted person, or encoded in a system only the original holder understood. Check the estate documents carefully for any reference to a "25th word," a "BIP-39 passphrase," or "additional security layer."

Exchange Accounts: When Bitcoin Is Held by a Third Party

If your family member held Bitcoin on an exchange, the inheritance process looks more like inheriting a brokerage account. The Bitcoin is technically held by the exchange; your family member had a claim against it. The exchange will likely require a death certificate, letters testamentary from the probate court, and their own account verification process.

Exchange-held Bitcoin carries different risks in inheritance:

• The exchange may freeze the account upon notification of death
• The exchange may have its own policies about inheritance timelines and documentation requirements
• If the exchange becomes insolvent — as several major exchanges have — the assets may not be fully recoverable
• Login credentials alone are rarely sufficient; exchanges typically require formal estate documentation
• Some exchanges require account verification that only the original account holder can complete (biometric, ID match)

If you discover exchange account credentials, secure them, and contact the exchange directly through its official website only. Do not use any login link sent to you by email or text message without verifying the sender independently.

Step-by-Step: Claiming Exchange-Held Bitcoin

Each exchange has a slightly different process, but the general framework is consistent across the major platforms:

1. Locate the account details. Username, email address on file, and the exchange name. Do not log in yet.
2. Identify the correct exchange. If you only have login credentials without knowing the platform, check browser saved passwords, email history (search for "[Exchange Name] verification" or "Your account"), or the estate documentation.
3. Navigate to the exchange's official website directly. Type the URL; do not click email links. Go to their support or "deceased account" page.
4. Initiate the estate claim process. Most major exchanges (Coinbase, Kraken, Gemini, etc.) have a formal process. You will typically need: a death certificate, a copy of the will, letters testamentary from the probate court, and identification for yourself as the executor or beneficiary.
5. Complete KYC for the receiving account. Most exchanges will require the estate beneficiary to pass Know Your Customer verification on a new account before any transfer is made.
6. Wait for the transfer. Timelines range from 2 weeks to several months depending on the exchange, jurisdiction, and documentation completeness.
7. Determine disposition. Once the Bitcoin is accessible in a verified account, coordinate with the estate attorney and tax adviser on the appropriate next steps — sell for distribution, transfer in-kind, or move to self-custody.

Multi-Signature Custody: When Multiple Keys Are Required

Some Bitcoin holders — particularly those with significant holdings — use multi-signature custody arrangements, often called multisig. In a multisig setup, a transaction requires signatures from more than one private key before it can be executed.

A common arrangement is "2-of-3": three keys exist, and any two of them can authorize a transaction. The keys might be stored in different locations — one with the owner, one in a safe deposit box, one with a trusted institution or collaborator. This provides redundancy (if one key is lost, the other two can still access the funds) and security (a thief who steals one key cannot move anything).

Common Multisig Configurations

The notation is always "M-of-N" where M is the required number of signatures and N is the total number of keys:

• 2-of-3: Most common setup for personal holdings. Three keys exist; any two authorize a transaction. Provides redundancy without excessive complexity.
• 3-of-5: Used for larger institutional or family holdings. More redundancy, higher security, but more complexity in inheritance if multiple keyholders need to coordinate.
• 1-of-2: Simple redundancy setup — two copies of the key or two separate keys, either can sign. Sometimes used for a primary and backup key.
• 2-of-2: Both keys required. Used when two parties (e.g., business partners) must both approve every transaction. Creates high security but also high recovery risk if one key is lost.

If you discover that your family member used a multisig setup, do not attempt to access the funds without locating all the documentation and understanding the full structure. Multisig inheritance is more complex and almost always requires professional guidance. The Letter of Instruction your family member left — if they prepared one — should describe the multisig configuration in detail, including which keys exist, where each is stored, and who holds them.

Collaborative Custody Arrangements

A newer category of custody sits between pure self-custody and pure exchange custody: collaborative custody. These services — offered by companies like Unchained Capital, Casa, and Theya — give the owner one or more keys while the service holds one key and provides infrastructure support.

The appeal is professional infrastructure without full trust. A typical 2-of-3 collaborative arrangement might be: one key with the owner at home, one key in a safe deposit box, one key with the collaborative service. The service never holds enough keys to move the Bitcoin unilaterally, but can assist with recovery if needed.

For heirs, collaborative custody is often the most accessible option:

• The service has a formal inheritance program and support process
• You do not need to understand the full technical setup to get started
• The service can coordinate transaction signing during the recovery process
• Professional support is available for the technical steps

If you find that your family member used a collaborative custody service, contact that service directly through its official website and explain the situation. They will have a defined process for estate claims.

Cold Storage Architecture: What Serious Holders Use

The term "cold storage" refers to any Bitcoin custody arrangement where the private keys are kept completely offline — never connected to the internet. Hardware wallets are the most accessible form of cold storage, but serious holders often build more elaborate architectures.

Understanding these setups matters for heirs because the more sophisticated the storage architecture, the more complex the recovery process — and the more critical the documentation.

Air-Gapped Signing

Some holders use hardware wallets in a fully air-gapped mode — the device never connects to a computer via USB or Bluetooth. Instead, transactions are transferred via QR code or a microSD card. The device signs the transaction while physically isolated from any network.

For heirs, an air-gapped setup may require a dedicated laptop or computer (sometimes referred to as an "air-gapped machine" — a computer that has never been connected to the internet) along with specific software. These items are sometimes stored alongside the hardware wallet and seed phrase.

Geographic Key Distribution

For very large holdings, some families distribute keys across multiple physical locations — a home safe, a safe deposit box in a different city, and a trusted attorney's office. This eliminates single points of failure: no fire, flood, theft, or natural disaster can compromise all keys simultaneously.

If you discover references to multiple key locations in the estate documents, treat this as a structured, intentional system that requires professional guidance to navigate properly. Each key location will have its own access requirements.

Custody Type Comparison Table

This table summarizes the key characteristics of each custody arrangement from the heir's perspective:

What Not to Do: The Rules That Protect Everything

Regardless of the custody arrangement you encounter, several rules apply absolutely.

The Bitcoin your family member held is protected as long as the keys are not compromised. The primary threat is human error — yours or someone else's. Go slowly. Verify everything. Trust no one you haven't independently confirmed through official channels.

Heir Custody Assessment Checklist

Use this checklist when you first learn that you're inheriting Bitcoin. Work through it methodically — do not take action on any item until you understand what you're looking at:

• Locate the estate documentation: Letter of Instruction, will addendum, or sealed envelope from the deceased
• Identify all custody arrangements documented (exchange accounts, hardware wallets, multisig, collaborative)
• Inventory all physical items: hardware wallets, metal seed plates, notebooks, USB drives, safes
• Document the location and condition of each item — photograph with date/time if appropriate
• Secure all physical items in one or more protected locations before taking any further steps
• Identify any exchange accounts and their login credentials — do not log in yet
• Note any references to: passphrases, 25th words, additional security layers, or "extra protection"
• Identify any trusted advisers or professional contacts specified in the documentation
• Contact an estate attorney to determine the legal framework for asset transfer in your jurisdiction
• Contact a Bitcoin-knowledgeable professional before attempting to access any self-custodied holdings
• For exchange-held Bitcoin: contact the exchange via official website, begin the estate claim process
• For collaborative custody: contact the service provider via official website, report the death and initiate their estate program

Frequently Asked Questions

Continue with Article 3: What to Do in the First 30 Days, or return to the Heir Education series overview for a full picture of the series.