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@fanoush
it is GND -> some transistor/FET marked Y2, switched by pin D14 -> one side of piezo -> 12ohm piezo/speaker -> 10ohm resistor -> VCC
so 22 ohm in total between VCC and GND when D14 is low (more precisely 22 ohm between VCC and top of the FET)
That is a bit strange because I=U/R = 3/22 ~= 136mA but I guess that battery cannot give more so the rest is internal resistance of battery
EDIT: attached picture - red are both sides of the speaker, R is 10 ohm resistor, V is VCC, G is GND
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