Tamper Proof Security Intrusion System

Tamper Proof Security Intrusion System / Burglar Alarm Tamper Proof Wiring

Information on Normally Closed vs. Normally Open circuits and
EOLR (Single End of Line Resistor) & DEOLR (Double End Of Line Resistors).

Normally Open vs. Normally Closed

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 jewellery 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 siren 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.

In an alarm system without resistors, a thief can bypass a sensor by cutting the wire on a normally open circuit, or by shorting the wires in a normally closed circuit. Using normally closed circuits with properly placed resistors makes it harder to bypass the sensor.

Below are diagrams indicating where to place Single End Of Line Resistors. The Normally Open and Normally Closed items in the diagrams represent the sensor and how it was wired.

Note: These diagrams show a simplistic version of wiring a sensor. Typically, 2 conductor wire is used to wire window/door sensors and 4 conductor wire is used on motion or glass sensors. It is not a simple loop of single conductor wire as shown above.

Tables below assume 5600Ω resistors are used.

Resistance	Normally Open Meaning	Normally Closed Meaning
0Ω	Zone violated. Sensor tripped - Alarm Activated	Zone fault. Wire shorted - Alarm Activated
5600Ω	Zone secure.	Zone secure.
Infinite Ω	Zone fault. Wire shorted - Alarm Activated	Zone violated. Sensor tripped - Alarm Activated

Double End Of Line Resistors (DEOLR) can also indicate if a wire has been cut. DEOLR only works with one Normally Closed sensor per zone. Do not use DEOLR for fire, supervisory and keypad based zones. For this to work properly, both resistors should be with the sensor - not in the alarm panel. Otherwise, tampering with the sensor by shorting it as shown above will successfully bypass the sensor. See below alarm wiring for examples.

Resistance	Meaning
0Ω	Zone fault. Wire shorted - Alarm Activated
5600Ω	Zone secure.
11200Ω	Zone violated. Sensor tripped - Alarm Activated
Infinite Ω	Zone tampered with. Wire cut - Alarm Activated

Other Security Measures

The last security measures to take are with the alarm panel itself. If an intruder is able to get to the alarm panel and disable it before the siren goes off or before it alerts the monitoring company, then the alarm is useless. Remember that opening a door doesn't automatically set off the alarm. By default you will have 30 seconds to enter the code to deactivate the alarm before the siren sounds. An intruder will also have 30 seconds to find and disable the alarm.

Purchase a lock for the alarm panel box if it did not come with one. Keep the alarm panel locked at all times. Do not store the keys on or near the alarm panel.

All alarm systems have a battery backup, but the battery might not be included with your system. Get the backup battery and keep the battery locked in the alarm box.

The alarm panel should not be visible through any windows (including small basement windows). It should not be placed near any entrance to the home. For example, don't place the panel in the mud room - the room off of the garage entrance. The room containing the alarm panel should be protected by sensors, or if there are no windows to that room, then the adjacent room could also be protected preferably by a motion detector.

Many alarm systems allow each zone to be configured differently. The door to the garage can be configured for a 30 second delay before activating the alarm to give you time to enter the code, while the motion detector that protects the alarm panel can be configured to activate the alarm immediately.

Be sure to change all default passwords for the alarm system - not just the master code, but the installer codes also. These default passwords are well documented and can be found by anyone.

If possible, hide the wires as they enter the alarm panel. For a basement installation I like to vertically mount two 2x4s to the concrete wall, and then mount a 2'x4' sheet of plywood to those studs. That gives me a good working area that I can easily drill screws into without having to deal with concrete. You can then run the wires behind this sheet of plywood and enter the alarm panel box through a hole in the back of the box. The sheet of plywood should cover up the wires near the top of the basement wall. From there I tuck the wires under the insulation that surrounds the exterior of the home above the concrete wall. Remember that this does not need to be perfect. You only need to slow the intruder down for a couple of seconds.

For first floor / drywall mounted alarm panels, try to run all of the wires hidden through the drywall and then through the back of the alarm panel box. You will not be able to hide the power connection (it would be a code violation to hide an outlet in the drywall), but this is OK since the battery backup should be locked inside of the panel.

Consider getting motion detectors or a glass break sensor. Window sensors only detect if the window is opened. Breaking the glass and going through the broken window doesn't set off the alarm.

ACTIVE INFRARED PERIMETER SENSOR

ACTIVE INFRARED PERIMETER SENSOR 

Perimeter sensors use infrared (IR), passive infrared (PIR) or light-detecting sensors to monitor your surrounding property. When movement is detected by these sensors, they can send notifications to your alarms or security system so you instantly know when someone is approaching.

An infrared (IR) sensor is an electronic device that measures and detects infrared radiation in its surrounding environment. Active infrared sensors both emit and detect infrared radiation. Active IR sensors have two parts: a light emitting diode (LED) and a receiver.

Active Infrared (IR) Fence Detectors, or Photoelectric Infrared Fence Sensors have been widely used in perimeter security systems. Unlike the electric fence, the Active Infrared fence detectors utilize invisible Infrared barriers to detect the intrusion. It has long detection/guarding range, low-cost, high-quality, and installation-friendly features. Some IR fence detectors adopt 4-channel frequency design to avoid IR interference between different beams, this can greatly reduce the false alarm rate to offer you accurate motion detection.

Some Active IR Fence Detector product portfolio includes 2∼10 beams, and detection range reaches up to 5m∼40m. These photoelectric fence sensors have N.O. and N.C. alarm output, can work with difference systems through reliable wired connection. It's the ideal security detectors for your intrusion alarm system, access control system, IP surveillance system and home automation system.

1# How active infrared fence detector works?

Each Active Infrared (AIR) sensor comes as a pair, consisting of a transmitter and receiver. IR transmitter emits multiple Infrared light to the receiver, this is the working principle of AIR sensors. The transmitter and receiver are installed opposite each other, the area between the transmitter and received has been guarded by invisible IR-beams. When a person or object crosses the IR-beam, the infrared beam is interrupted. The receiver triggers alarm and send alarm signals.

AIR fence detectors use an active infrared technique, it provides much accurate motion detection than PIR-based detectors. Additionally, the fence sensors use the pulsating code to filter out interference light sources from sunlight,car headlights and lightning flashes. The fence receiver only reacts to interruptions in this pulsating infrared beam, other light sources therefore do not affect the receiver. Our active Infrared fence detectors emit IR in 4 different frequencies to make it difficult to be replicated and interfered.

2# How to choose right AIR fence detectors?

To choose the right active infrared fence detectors, you need to consider the following two things; the number of beams, the detection range. Most active infrared beam detectors have 2, 3, 4, 6, 8, 10 beams. The more the number of beams, the higher of the detector's height.  Typically, 2∼4 beams fence detectors are suitable for covering single window and door. 6∼10 beams AIR fence detectors fit the application of balconies and windows and doors in the array.

Active Infrared Fence Detector Installation 1

AIR Fence Detector Installation 2

Detection coverage/range is the another very important factor when choosing the detector. Unlike other detectors, the installation distance between the transmitter and receiver should be the exact/approximate same rated detection distance of Active Infrared fence detectors. This means if the detection range is 20 meters, users need to choose 20 meter Active IR fence detector, not the 40 meters product. However, the Active IR detectors allow users to adjust the intensity of Infrared light to change the detection distance.

3# How to connect the AIR fence detector?

Both IR transmitter and receiver requires power supply (10.5 - 15V DC) to operate. However, sync connection maybe required for the long range detection. When connecting the AIR fence detector to alarm systems, EOL resistor (2.2Kohm) connection is mandatory to supervise the circuit.

Note: In order to avoid false alarm caused by power failure/electricity outage, it's recommended to use UPS power supply.

Note: If the controller is an alarm panel, EOL resistor (R1) should be used, it should be connected in series to protect and supervise the circuit. Other controllers don't need to use EOL resistors.