Is your person still active?

Paste your guardian packet (the NULLDMS1.… line they gave you). Your browser derives their sealed heartbeat mailbox and checks for recent signs of life. You learn nothing else — heartbeats carry no content.

How this works. Their device posts a tiny sealed heartbeat whenever they use NULL (every ~45 minutes while it’s open). It also leaves sealed check-ins ahead of time, timed to secret moments only you and they can compute — so a check here tells you when they were last active, up to a week back, even if they are not online right now. You do not need to check daily: check when you are worried, or about once a week. A last-active time that keeps getting older — or none at all in the past week — together with being unreachable every other way, is the signal to act. (If their NULL app has not been opened since this feature arrived, only the live last-hour check works; the page tells you which you are seeing.) The message itself was split with Shamir secret sharing when they set it up: fewer than the required packets reveal nothing, mathematically. NULL’s servers cannot read heartbeats, cannot see who checks, and never held the message.

Guardians hold real power: enough of you together could open this early. They trusted you not to.