Homemade anti-theft watchdog

This article introduces a simple home anti-theft watchdog circuit (see the figure below).

The time base circuit NE555 and R1 and CL form a monostable trigger. Normally, when C1 is fully discharged, the 3rd pin of NE555 outputs a low level, and the dog barking integrated circuit KD5608 does not work. M is a touch piece, which can be replaced by the lock body of the door lock. When an uninvited guest touches the door lock, the stray voltage induced by the human body acts on the 2nd pin of NE555, the monostable circuit is triggered to flip, NE555 outputs a high level from the 3rd pin, and the dog barking integrated circuit KD5608 is powered on and works, outputting a dog barking audio signal to the 3rd pin of the audio power amplifier LM386. After LM386 amplifies it, it drives the speaker to emit a loud dog barking sound, so that the uninvited guest retreats. After that, the power supply charges C1 through RL. When the voltage on C1 is charged to higher than two-thirds of the power supply voltage, the monostable trigger flips again, the 3rd pin of ICL outputs a low level, the dog barking integrated circuit KD5608 loses power, and the speaker stops sounding. If you think the barking of dogs is too noisy when your family members unlock the door during the day, you can press K at night so that the circuit will only function as an anti-theft device at night.