Bomb squads have drones to get a look from a distance, and equipment to sniff out chemical compounds - is it anfo, plastique. Is there a timer, or is it attached to a cell phone or the like that can be jammed or have cell service temporarily brought down.

For real dude, bomb squads don't exist to shrug their shoulders. You don't know how much time there is. Bomb gets called in and you don't go "well, it'll probably go off before we get there so why bother". Why even have a bomb squad then??

"Operator there's a knife wielding maniac who just broke into my home!"

"Well, we'd send someone, but what would a patrol car have time enough to do exactly?"