What a deadman switch actually is

A deadman switch is a piece of machinery that does something when the person holding it lets go. Train drivers have had them for a century: keep the lever pressed and the train runs, release it and the brakes come on. The switch does not detect danger. It detects the absence of you.

A vault here works the same way. You write a message, optionally attach files, name one recipient, and choose how often you intend to check in. From the moment you arm it, a clock runs. Pressing Check in resets the clock to full. If the clock ever reaches zero, the message and its attachments are emailed to the recipient, and the vault is marked as delivered.

That is the whole mechanism. There is no judgement in it, no attempt to work out whether you are really in trouble, and no human deciding whether to send. The only question it ever asks is whether you checked in before the deadline.

What this is good for

It suits anything where the cost of nobody ever finding out is higher than the cost of a false alarm:

• Passwords, account recovery details and the location of documents that your family would otherwise spend months reconstructing.
• Instructions that only matter if you are not there to give them: what to do with a business, a pet, a server, a storage unit.
• Evidence, notes or records that a journalist, lawyer or colleague should receive if you go quiet.
• A letter you want a specific person to read, that you would never post while you were able to speak to them yourself.

What it is not

It is not an emergency service. If your deadline is seven days away and something happens on day one, nothing is sent for six more days. If you need someone alerted within minutes, a deadman switch is the wrong tool and a person with your phone number is the right one.

It is also not a substitute for a will. Delivering a set of instructions to a named person is not the same as an enforceable legal document, and no email from us confers any legal authority on the recipient. Use it to make a will easy to act on, not to replace one.

The one thing people get wrong

The interval is not a measure of how urgent your secret is. It is a measure of how reliably you can press a button. A one day timer on a vault that matters is a promise to check in every single day for the rest of your life, including the weekend you spend somewhere with no signal. Most people who set a one day timer end up triggering it by accident within a month.

Pick an interval you can keep on your worst week, not your best one. A month is a perfectly sensible answer for most people.