Simple DIY laser alarm

Question

Im begginer and currently Im trying to make DIY laser alarm (while laser is pointing at LDR sirene should remain silent and when laser is turned off, sirene should make sound). I found online following schema

As sirene Im using KPE212A for transistor I have bc337-40 and LDR is VT43N1

Problem is that instead of sirene going on/off based on laser pointer, I get only change in pitch of sound (Sirene is constantly on, but only increases its volume while laser is pointing at LDR). Could you please advice what is wrong and how I could fix it ?

Answer 1

The resistance of the LDR does not drop low enough to turn off the buzzer.

So you can try something like this:

^{simulate this circuit – Schematic created using CircuitLab}