A simple circuit diagram of a home security door alarm

The finished anti-theft devices or facilities on the market have great defects, not to mention simple self-made anti-theft devices.

For example, the human body pyrothermal infrared detection alarm, commonly known as infrared detector, is the white half-garden column, in the summer when the temperature reaches more than 30 degrees, because the temperature is close to the human body temperature, and the human body temperature is 37 degrees, but the appearance of the temperature is only 32 degrees, plus sweat evaporation, probably only 31 degrees, the infrared detector has been difficult to detect the temperature of the person, the alarm fails. Through experiments, it is measured that when the temperature is 30 degrees, the detection distance is less than meters, and when the temperature is 32 degrees, the detection distance disappears, and there is no alarm effect. At 25 degrees, when the human body makes longitudinal movement of the pyrothermal infrared detection alarm, that is, it is slowly approaching the infrared detection window, only to close the alarm, without any reflection, and only when the lateral movement is made, the alarm will be alarmed.

Therefore, it is unreliable to use infrared alarms in summer.

There is a kind of window protection radar, placed on the outdoor window, not radar, in fact, it is a human pyrothermal infrared detection alarm, in more than 20 degrees, due to the sunlight, the internal temperature is difficult to dissipate, the detection chip loses its detection effect, these things are tested indoors when they are bought, they are very smart, but in practical application, it is not that good.

In some places, the human pyrothermal infrared detection alarm is also placed on the courtyard wall, which is the kind of dark color, which is easier to cut and destroy the wire.

A door and window alarm with door magnetism, a little narrower than a match, relatively simple to make, pasted on the door and window, but not used in summer, pasted on the screen window in summer, easy to be cut off the screen to close the alarm, thieves are still easy to come in.

There are also infrared rays and reflection fences, in addition to being detected with infrared glasses, you can hear the "answer" sound when you approach it with a small radio, and it is cracked, so I advise you not to make it yourself.