Will this sensor work with arduino? I'm building an electronic gate. I'm needing a photoelectric sensor to detect cars. This one in the link looks decent. it runs on 12v so I will need to power it separately from the arduino. But does this mean it also puts 12v back to the signal wire? Will that work with ardunio without burning the circuit? How many V can i send into an arduino pin?

thanks

photo electric sensor
The sensor you specified states:

Output: SPDT Relay Output


If accurate, it may be inferred that the output is simply 3 contacts where one is normally open and the other is normally closed and the 3rd is the common.  If true then you can treat the output as if it were an ordinary Single Poll Double Throw (SPDT) switch.  Note, with regard to processors, an ordinary switch may need to de-bounced.  This depends on how the state of the switch is used.