Possible Clues:

• Device to sense when to turn off includes time in firm
• Airport security device
• Sensor
• Smoke __
• Sensitive type is alarmingly looking for drugs perhaps
• Sees right through you as, in retrospect, didn't last long around church
• Device warning of, eg, smoke
• See 46-Down
• One picking up Edward coming back without a lead for 12-across
• Electronic device went off around church when installed the wrong way