Burglar alarm system having reduced wiring

An alarm system comprising a cable (11l) between an alarm panel (10l) and a sensor (12l), which cable (11l) consists of only two conductors, and circuitry (13C) associated with said conductors to provide power the sensor (12l) through said conductors and detecting a change in said stream through by said conductors to indicate tampering at the sensor, a cable cutting and / or an event detected by the sensor, wherein the sensor is an event sensor (12l) responsive to movement of a person in an area where there is the sensor event, to increase the through-flow through the conductors, characterized in that said circuitry (13C) is located in a housing from which extends the two-conductor cable (11l) and is set a short six-conductor cable (11) for connection to a control panel existing alarm (10l).