One of the touch anti-theft alarm circuits

It uses sound-producing devices such as semiconductor radios to achieve alarm. It's actually an electronic
switching circuit. When used as an anti-theft alarm, the metal sheet cover is installed on the anti-theft items.
    It uses triodes as control components and contactless switches.
    When the finger touches the two metal sheets Mi, the circuit is connected,
that is, the alarm (radio, etc. sounds). To turn off the circuit,
just touch the two metal pieces M2.