Function of an electronic circuit

[johnbaker]

Hello, I need to understand the exact working of an electronic circuit (see picture) but I am very bad at electronic. This is the electronic circuit of a personal alarm that triggers an alarm when you pull out a metal part (like a grenade). All I know is that when you remove the metal part (that looks like a piston) from , the metal disk on the left (which is a piezoelectric disc) produces a loud sound. I would like to know what exactly happens. What is the part that transform the electricity from the battery to an "alternative" current that makes the piezoelectric vibrate ? Thanks a lot to anyone that could help me

 

[Harald Kapp]

Likely the chip labeled U! next to the plug mechanism. You need to supply a better photograph to identify the chip. Or read the labeling on top of the chip and post it here. Could be something as simple as a 555 timer chip.
The assorted chips at the top are probably for driving the LEDs and for charging via USB.

 

[johnbaker]

Likely the chip labeled U! next to the plug mechanism. You need to supply a better photograph to identify the chip. Or read the labeling on top of the chip and post it here. Could be something as simple as a 555 timer chip.
The assorted chips at the top are probably for driving the LEDs and for charging via USB.

Thank you very much for your help. I attached a picture of the chip but nothing is written on it. After having checked on the internet, i think it is a 555 timer chip but there should be something written on it... And do you know what is the use of the black cylinder at the left of the plug ? I attached a clearer photo of it too.
Thanks a lot

 

[Harald Kapp]

Not uncommon for manufacturers to erase or paint over the labeling to "protect a trade secret".
The black cylinder looks like an inductor. As to its function in the circuit: no clear idea. It seems to be in the circuit that drives the piezo. It could be parallel to the piezo to create a resonant circuit. By using resonance the amplitude and thus the volume of the alarm would be increased.