| 摘要 |
<p>A fire callpoint (10) is disclosed in which a light source (24) and a light receiver (26) act as a switch to establish an alarm condition. In the callpoint's normal, dormant condition light can either reach the receiver or not reach the receiver. Upon activation, light is either cut off from, or falls upon, the receiver changing the status of the fire callpoint to its alarm condition. Breaking or distorting a transparent cover (30) is employed to deflect light onto, or away from, the receiver or to obstruct a light path so that light ceases to reach the receiver or to establish a light path so that light reaches the receiver</p> |
