Try the tool

Runs in this page. Your inputs are not uploaded or saved. Dates use your browser’s time zone.

Your result

Add the available duration to a completion time to see the example clear time. This does not change the app or predict a lock's state.

A worked example

A check completed at 8:46 AM with an eight-hour duration has an example clear time of 4:46 PM on a day without a clock change.

Elapsed hours across a clock change

The calculation adds actual elapsed hours, not a wall-clock calendar day. Daylight saving changes can make a 24-hour interval display at another local clock time.

Earlier clearing in the app

A new check, adding or renaming an item, or enabled Reset when I return can clear the current check sooner. An existing receipt's duration is fixed when it completes.

Keep the next check on your iPhone

Create the items manually in Is It Locked?. This browser draft does not transfer into the app. Check the items yourself, then record them.

Get the app free

iOS 27 or later. One place and one list are free.

The app records what you checked. It does not lock doors, switch off appliances, or verify their physical state.

Sources and review notes

Calculation conventions and boundary cases are documented above. The tool runs locally and is tested against arithmetic and calendar examples.