How to Install Electric Bells, Annunciators, and Alarms. / Including Batteries, Wires and Wiring, Circuits, Pushes, Bells, Burglar Alarms, High and Low Water Alarms, Fire Alarms, Thermostats, Annunciators, and the Location and Remedying of Troubles

by Norman H. Schneider

Door Trip Alarm.

A swinging contact door trip can be attached over a door to ring a bell when the door is opened.

Fig. 51

In [Fig. 51] the door trip is screwed over the door so that the lowest arm A is struck by the door. When the door is opened, in the direction of the arrow, the arm A is thrust forwards, and in its turn moves the contact arm C, completing the bell and battery circuit. But when the door is being closed, A swinging in the reverse direction does not move C and no alarm is given.