Tamper Proof Security System / Burglar Alarm Wiring | CCTV Training Oman

 

While no wiring can be completely tamper proof, there are a couple of things you can do to make disabling your alarm system more difficult. These methods may not be enough to protect a business like a jewelry store, but they are more than adequate to protect your home from a common thief. 

  The first thing to do is to use normally closed (NC) circuits when possible. Most alarms and sensors by default are configured this way. To understand why you should first understand how a common window sensor works. An open circuit is a broken, interrupted, or incomplete circuit. For alarm systems, a normally open (NO) circuit is in the open state when the alarm has not been tripped. Closing the circuit sets off the alarm. A closed-circuit is a connected and complete circuit. A normally closed circuit is closed when the alarm is not active. opening a normally closed circuit sets off the alarm.

  The circuit below is an over simplified example of a Normally Open alarm circuit. When the switch is open under normal conditions the circuit is incomplete and the sired will not sound. When the switch is closed then the circuit becomes complete. The connection from the battery to the siren is complete and this activates the siren.

  Window sensors are the best way to show a real alarm circuit in action. A window sensor consists of 2 parts. The first is a magnet that is attached to the part of the window that moves. The second part has the wire connections and should be mounted to the frame around the window or to the part of the window that doesn't move. When the window is closed, the two parts of the sensor should be right next to each other.

  The wired part of the sensor contains a switch that can connect to two different contacts. When the magnet is near this switch, the magnet will attract the switch toward the normally closed contact. When the magnet is removed (because the window has been opened), the spring pulls the switch toward the normally open contact. You will connect the common contact and either the Normally Closed (NC) or Normally Open (NO) contact to your alarm system. 

  When using the normally open (NO) contact, the connection between the common (C) and NO contacts is broken when the window is closed. When the window is open the magnet is removed and the spring pulls the switch toward the Normally Open contact which closes the circuit and activates the alarm.

  One of the drawbacks with Normally Open circuits is that cutting the wire will deactivate the window sensor. With a Normally Closed circuit, cutting the wire will set off the alarm. With a Normally Closed circuit, opening the circuit will activate the alarm and opening the window or cutting the wire has the same effect.

Single and Double End Of Line Resistors

   

Adding resistors to the sensor circuit path allows the alarm panel to determine more than if the circuit is simply open or closed. It can be used to differentiate between an active alarm, alarm tampering by cutting a wire, and a short in a wire. Note that End Of Line Resistors (EOLRs) can only be used if the alarm panel has been designed to use them. Consult your alarm manual before using any resistors. The diagrams below and resistance values may not apply to your alarm panel.

  Single End Of Line Resistors (EOLR) are common with monitored alarms so that the monitoring company can differentiate between a cut wire and a tripped sensor. Some installers will place the resistor in the alarm panel but this not correct. The resistor should be placed at the sensor to better detect cut wires.