For my school I want to make a system where you can check if the bikes are returned to their place. For this I need a System where the bike has an identifier which is connected to some sensor if it is at the right place. Does anyone know what sensor to use for that or an other idea to solve the problem?
Barcode scanner, RFID tag and reader, simple hall effect sensor, there are many sensors that may fit your project but you haven't specified what limitations you have or what you want to check (p.e. have the bike to be identified or does any bike fit?).
The bike need to be identified.
RFID tag seems an obvious choice - but the range is pretty short, which may be an issue.