bauerbyter:
There is only a resistor in the connection to Vcc in the Datasheet (ApplicationCurcuit)
Do i also need a pullup?
If I read the datasheet right, "Output Active Low", then you should get a more reliable signal by using a pullup resistor.
Good news though, rather than physically wiring in a separate component, you can enable the Arduino's internal pullup resistor on the appropriate input pin. Simply change 'INPUT' in your pinMode command to INPUT_PULLUP.
EDIT: I should have looked more closely. The datasheet block diagram shows a 30k pullup resistor inside the receiver IC already. So a pullup on the Arduino would be unnecessary.