Alarm system for taxi phone preventing unauthorised removal - with line circuit connected to police station operated by tampering

摘要

The taxiphone is located in a box, which is opened by a pass key and attached to the base of the box. Any attempt to remove the taxiphone causes a contact (231) which is normally closed, to open and operates a telephone link to a local police station (P), the link normally being balanced by an adjustable resistance (24) incorporated in the taxiphone and in series with the contact. Alternatively a normally open contact in series with a relay operating circuit may be employed, with the relay contact operated to release an alarm signal. The relay operating circuit may be supplied via the same telephone line or via a supply battery incorporated in the taxiphone.