| 摘要 |
The device is installed in a tubular housing (1) which is fixed horizontally to an object, e.g. a wall, door, pillar, vehicle, etc. A proximity detector (10), e.g. an infra red sensor, detects the arrival of a person within 2.5 metres of the device. The detector triggers circuits which cause a pre-recorded message to be read out of a solid state memory and converted to analogue form. The analogue message is amplified and fed to loudspeakers (7) at both ends of the housing. If an attempt is made to tamper with the device, an alarm circuit (12) operates.
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