Theft Detection Lock and an alarm app

Theft Detection Lock is part of Android's theft protection settings. It uses the phone's motion sensors, together with Wi-Fi and Bluetooth signals, to recognise the pattern of a phone being grabbed and carried away fast, on foot, by bike or in a car. When it recognises that pattern it locks the screen, so the person holding the phone cannot use whatever app was open.

It comes with two companions. Offline Device Lock locks the screen when the phone is disconnected from the internet for a while, to stop a thief going offline to avoid tracking. Remote Lock lets you lock the phone from a browser using your phone number, even if you cannot sign in to your Google account.

According to Google's help page, these need Android 10 or later, a screen lock, and Google Play services, and availability depends on the phone model. You turn them on under Settings, Google, All services, Theft protection.

Theft Detection Lock is silent. It does not sound an alarm, draw attention or make the thief drop the phone. It acts after the theft has succeeded, and its goal is to protect your data and accounts, not to get the phone back.

It also watches for one kind of theft: a phone snatched from your hand or pocket while you are moving. A phone lifted from a café table, unplugged from a charger at the gate, or taken from a bag while you sit still does not produce the motion pattern it looks for. Google is open that it will not catch every theft, and that it may occasionally lock the phone when you are just running for a bus.

Finally, it takes no photo and records nothing about who took the phone. If you want evidence, or you want to hear it happening, you need something else.