| 摘要 |
A security arrangement for electrically powered, alarmed, mobile units having an internal electric power supply 12 which connects 14, 16 to auxiliary or alternative external power supplies comprises an alarm actuating circuit 22, 29 adapted to detect disconnection of the unit from an auxiliary or alternative external power supply and to actuate alarm means 25 of the unit on detection of such disconnection. The unit may be a caravan, a boat or a hut. The arrangement gives a warning of theft of the unit. Circuit 22 detects the voltage existing between the neutral and earth conductors or an external a.c. mains power supply, which disappears when connection 14 is broken. Circuit 29 detects breakage of connection 16 to a d.c. voltage from e.g. a car battery. <IMAGE> |
