Device asks for pin

Hi...

For a couple of weeks my good old Nexus frequently asks for the pin code. Especially while driving in my car. Sometimes it also happens when I carry it around in my pocket.

I changed the battery but without any effect.

Sounds funny, but I have the feeling, it always happens at the same location while commuting.

Has anyone an idea? Might resetting the device to factory defaults help?

Thanks in advance....