Not a clue, but I’ve never use my thumb to lock the doors. A thumb print is a bit different and more curved than fingers - perhaps the beep indicates the sensor is initially having trouble confirming it’s a print? Something to ask a Toyota dealer perhaps?

Hi Mike,

It will most likely be something on the back seat, open windows, or the car is not close enough to the key, mine does it quite often when I have items like dog beds on the seats. I think it just a warning to check you haven't left the kids in the car 🤣

Kind regards,
Val 😊

Nothing to do with the actual thumb print. Any finger or part of the hand will do. A beep indicates you have left something on in the car.
I use this all the time. For info, one touch locks the doors but if you touch it again within five seconds it activates the deadlocks.