Could my security light have been tampered with?

Possibly, Burglars do regularly target security devices although with security lights they usually try and switch them off (normally by breaking them or moving the sensor). there are cases where the burglar will deliberately keep setting devices off (alarms being a big one) in order to annoy the occupier and make them believe it is faulty, this way the owner then switches the device off themselves... Check your light and make sure it has not been tampered with. If you cannot see anything unusual then it may just be a fault but obviously be vigilant and get it fixed asap.