Ma-Ma has this thing attached to herself which will detonate the bombs if her heartbeat stops. Well she does die in the end and yet the bombs don't go off. Did I miss something here?
Dredd reasons that the detonator's signal will not reach the explosives from the ground floor, so he forces Ma-Ma to inhale Slo-Mo and throws her down the atrium to her death. (Source: Wikipedia)
So its clear that building doesn't blow up because of signal range.
I think this is a major plot hole. Any decent Dead Man's Switch system would trigger the detonation when the receiver fails to receive a signal (unless of course the receiver is disarmed).
Failure to receive a signal can be caused by all sorts of things: Ma-Ma's heart stopping, the transmitter being removed from her arm, being destroyed, losing power, being jammed, or going out of range.