An encased magnetic reed switch is held open by a magnet so that when the magnet is moved away such as in the opening of a door or window the switch closes. This initiates a warning sound through an inbuilt sounder. This circuit has an optional, adjustable inbuilt timer which may be switch selected to regulate the duty cycle of the sounder device.

Technical information.
- Requires power supply : 9V
- Current consumption : 40mA ( max )
- PCB size : 3.27" x 1.57"

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