What happens if you are being tracked using an AirTag but you don't own an apple device?
It makes a sound.

An AirTag that isn’t with the person who registered it for an extended period of time will also play a sound when moved so you can find it, even if you don’t use an iOS device.

What to do if you find an AirTag or get an alert that an AirTag is with you - Apple Support, emphasis mine

after an AirTag has been away from its paired device for a certain amount of time, the item will automatically emit a sound notifying those around it of its presence.

An Apple executive, quoted by 9to5Mac in Apple execs explain how AirTag is ‘stalker-proof’ and whether you should use it to track pets