There is nothing in the standard that says you must or must not have flashing leds. Most modern hardwired BB do have flashing Leds, most wireless dont. There are hard wired box's available without Leds. It depends on what type of intruder you are likely to get as to whether he will even notice if you have an alarm, a professional burglar will have done his homework, and a drugged up opportunist wont notice the bell at all until its ringing.