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Ultra-Sonic Burglar Alarm System

Ultra-sonic alarm system is a silent alarm inaudible to humans. The siren emitting from it lies in the ultra-sonic frequency and therefore cannot be heard by humans. Generally, banks use this type of alarm system. So far as home security is concerned, using such a setup requires a quick response team as well.

Mechanism:
Inside a home, the device makes use of sound waves. These sound waves act as motion sensors. The waves get projected in the form of beams. The beams bounce across the surface area of the room. Commonly used detector beams are passive infrared beams. They can detect not only activities but also changes in temperature. Using a coverage lens, the beams get projected into a room’s space. The dispersion of beams throughout the room depends on the configuration of the lens. Due to the sensitivity of the system, however, false alarms are caused by heating systems and sunlight. Therefore, the system must be adjusted and positioned properly.

Function:
The sound waves in the ultra-sonic range vibrates so fast at such a frequency that human ear cannot detect them. This is why they are called ‘silent’. However, animals like dogs and mice can hear high frequency sound. Therefore, they are able to detect and hear ultra-sonic alarms. The air molecules in these series of sound waves are subjected to repeated compression and expansion. The resulting cyclic vibrations in which they travel are called frequencies. Number of cycles per unit time is defined as frequency and is measured in hertz (Hz). One hertz equals on cycle per second.
The ultra-sonic waves travel above 16,000 Hz. Human ear can only detect frequencies between 16 to 16,000 Hz. Such high frequency waves are directed or focused into narrow, straight beams. These beams are like trip wires in security systems. They detect and pick up changes in vibration caused by body heat or motion in the room. Therefore, the presence of any intruder is detected without the intruder knowing it.

Considerations:
The thief, on entering the house and activating the alarm, does not realize the presence of security system, till the arrival of the police. However, the police must arrive quickly or at least early enough before the thief leaves with the booty. The only way, he gets warned will be by the flash of light that too if it is in his line of sight.
Since there is no noise heard in this alarm, neighbours and owners of the home are not warned and therefore, chances of the thief leaving before help arrives are high. In case of audible alarms, everyone can hear the alarm including the thief. Hence, while the intruder is warned of the existence of an alarm, the people in the locality are warned of the existence of an intruder.

Some wise home security system companies use a combination of ultra-sonic and normal devices. In such devices, there is an audible siren that starts ringing the moment an abnormal activity is detected by the ultra-sonic beam.

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