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BTS Shelter

Magnetic Switch

Magnetic switches are the most common sensing devices for sensing opening and closing of doors and windows. They are cheap and reliable.

Such sensors consist of two parts - A contact switch that is installed on the door / window frame and a Activating magnet that is mounted on the door. The magnetic switch is held in no-alarm contact position when door / window is kept closed. These are installed on a door or window in such a way that opening the door or window causes the magnet to move away from the contact switch which activates the alarm. They have proved to be a tried and tested method of monitoring any of the operable openings in the houses / apartments. These contacts are available in variety of finishes & materials. Heavy duty versions are also available for heavy doors, shutters and gates. The magnetic switches normally have both 'Normally open' & 'Normally Closed' contacts for easier integration with existing systems. While installing care should be taken that alarm should go off when the door just opens. If the sensor is wrongly placed then it is feasible that a person may be able to squeeze in without activating the sensor. A series of such sensors can cover the whole house including every door / window / ventilator. The Magnetic switches need to be connected to Control unit (26), which senses the change in the position of door and activates an alarm.

In Wireless Systems (29), the principle is the same except no wires are required to connect the sensor to the Control Unit (26).

In cases a window has to be left a little open for ventilation, it is made possible by using 2 magnets and 1 switch. In this configuration the first magnet is mounted in the window closed position and the second is mounted in a location where it will align with the switch when the window is open a few inches, typically 3 or 4 inches. This allows for ventilation but will sound the alarm if the window is fully opened. Window or wall mounted air conditioners and Coolers may also require protection if they can be easily removed from the opening. The standard method used to protect these units is to install a sensor on the unit.

Advanced Version

For more sensitive control of the door, there is an advanced version called Balanced Magnetic Switch, in which the electrical contact of the switch is held in no-alarm condition by two magnets - one is fixed to the door frame and the other magnet is fixed to the corresponding position on to the door. As long as the magnetic field remains balanced with the door firmly closed, the contacts within the switch would be in no-alarm condition. Even with a slight movement of the door from the door frame the magnetic field gets unbalanced causing the Control Unit to sound an alarm. The balanced magnetic switch is more tamper-resistant than a simple Magnetic switch but requires higher skill and time for installation.

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