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.
Miscellaneous Alarms.
The Applegate electrical matting is composed of wooden slats with springs so arranged that the weight of any person stepping on it will close a circuit and ring a bell.
It is intended to be put under the ordinary door mat or under stair and room carpeting.
The Yale lock switch is a Yale lock and switch combined. Upon any key but the right one being inserted, a circuit is closed and an alarm bell is rung.