| 摘要 |
A signalling device comprises means for storing electrical energy <I>eg</I> a battery (41) connected to signalling means (48) <I>eg</I> an LED, and control means (45) to prevent actuation of the signalling means when charging current is supplied to the storage means but activate the signalling means if that current falls below a threshold. The control means comprises an oscillator (45) which is prevented from oscillating when the current is above the threshold. The current may be supplied to both the storage means and the oscillator via a pair of parallel diodes (D1,D2) from a solar cell connected across terminals (35), and the signalling means (48) may be a visual or audible alarm or an emergency light which is operated when ambient light level falls. Alternatively the oscillator may be controlled by a pressure contact to indicate low pressure in a fire extinguisher, or by the presence or absence of water between electrical contacts to indicate low water level.
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