A Lock Has Low Battery
Replace the batteries. There’s nothing to fix in software, and a lock that dies is the failure mode most likely to leave a guest standing outside.
Two things can trigger the warning
Your lock’s manufacturer decides when to report low battery, and that report reaches you as soon as it happens. Separately, GuestsKey checks battery levels every couple of hours and flags anything under 25%, at most once a day per lock so you’re not pestered.
That means the alert you get and the percentage on your dashboard won’t always agree, and the same lock can warn you through either path. The dashboard badge uses the 25% line — green at half or better, amber under half, red under a quarter.
Why to treat it as urgent
A weak battery doesn’t fail cleanly. Before it dies, the lock starts dropping off Wi-Fi, which shows up as the lock going offline and codes failing to apply. So a battery warning often arrives alongside other symptoms that look like a connectivity problem, and people go chasing the router.
If a lock is misbehaving and it’s also low, change the batteries before you debug anything else.
Practical notes
Most smart locks take four AA batteries. Replace all of them together, not the weak ones — mixing old and new gives you a short second life and another alert.
Lithium AAs last considerably longer in cold weather, which matters if your locks are exterior and you manage anywhere with a real winter.
If a lock is chewing through batteries in weeks rather than months, that’s not normal. It usually means the lock is straining to hold a weak Wi-Fi connection, or the deadbolt is misaligned and the motor is working hard on every throw. Worth fixing the underlying cause rather than restocking batteries.
There’s no notification when a battery is healthy again — check the dashboard after replacing them.