Invisible Burglar Alarm. Beginners Trial 2

You can easily make this Invisible Burglar alarm using Infrared LED and a Phototransistor. When there is no obstruction in the path of IR rays, alarm will be silent. When somebody crosses the IR beam, alarm sounds. If the IR LED and Phototransistor are enclosed in black tubes and aligned perfectly, the range of the circuit is around 1 meter.
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Simple Heat Sensor. Beginners’ Trial 1

Here is a 3 component Heat sensor. You can attach it with the heat generating devices like CD player, Inverter etc. When the heat inside the cabinet of the device increases above the set limit, buzzer beeps.
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