How to make a digital time capsule

What is a digital time capsule?

A digital time capsule is a set of files you deliberately keep out of reach until a chosen date. The idea is old: the Wikipedia article on time capsules covers the history of sealed containers. The digital version swaps the box for files and the burial for a lock.

The quality of a digital capsule depends on two things: how well the lock holds, and whether you can still open the files when the day comes.

What should I put in it?

Aim for six to ten items across the senses.

• A letter written the same day you seal.
• Three to five guesses about the open date, written so they can be checked.
• Two photos of ordinary things, such as a desk and a street.
• A voice note describing the week.
• Screenshots of your home screen and your most played songs.
• The prices of three things you buy often.

Plain files last longer than clever ones. Prefer JPEG, PDF and plain text.

How do I make one in Sealday?

Sealday is an iPhone app built for this. It encrypts the contents on your phone with AES-256, then locks the key to the public drand beacon, which publishes the key on the open date and not before. Changing your phone clock does nothing. The mechanism is explained on the time lock page.

A capsule can hold guesses, a letter, photos, a voice note and a "then" photo. There is no video and no account. Free capsules take one photo and a 30-second voice note, and Plus raises those limits.

1. Tap Seal and choose For future me.
2. Pick the date: New Year, your birthday, one, five or ten years, or any day from tomorrow to twenty years ahead.
3. Add guesses, a letter, a photo or a voice note.
4. Review the summary and press and hold the wax seal for about two and a half seconds.
5. Export a vault file from You > Backup and restore.

How do I stop myself from opening it early?

Willpower is a poor lock, which is why the table above ends with a mechanism. If you use a folder, give the password to a friend or move the files to a place you cannot reach without effort. If you use Sealday, a capsule for yourself has one emergency exit: Break the seal, type OPEN EARLY and wait 24 hours. The capsule then wears an Opened early stamp for good. A capsule you send to someone else has no exit at all.

That stamp is a small bit of honesty, and it makes the rest of the capsule worth trusting.

How do I make sure the files survive?

The date is the easy part. Files rot through lost phones, closed accounts and formats that stop opening. Keep two copies in two places, check them once a year and avoid files that need a special app. The Wikipedia article on digital preservation lists the kinds of risk involved.

For Sealday, the vault file is the second copy. It holds every capsule in sealed form and stays closed, so keeping a copy does not weaken the lock. See backup and restore and how to keep digital memories safe.

What should I keep out of a digital time capsule?

Sealday keeps your content encrypted on the phone and has no servers that receive it, but a letter is still a poor place for things that go stale. Write about the present and let the present expire on its own.

• Passwords, bank details and anything that expires. They will be useless or risky by the open date.
• Other people's secrets or private photos.
• Large collections you will never watch. Ten good items beat a thousand.
• Anything you would not want read aloud at your own birthday.

Which date should I choose?

One year for a first capsule. It is short enough to remember writing it and long enough for real change. Move to five years after you have done it twice, and treat anything beyond ten as a project with a backup plan. How long to keep a time capsule sealed goes through the trade-offs.