I bought a Movement monitor few days ago. How the monitor works was that when it doesn't detect a movement in 20 seconds, the small build-in speaker beeps (only beeps when alarm is on) and the voltage though it was roughly 1VDC as I measured. In order to get more than 5 volts to flash my micro controller when alarm turns on (it needs >3V), I just simply built a non-inverting 741 op amp with voltage gain of 5 (Vout=Vin*(1+R2/R1), Supply Voltage + = +9V, Supply Voltage V- = -9V. I intercepted a wire from the speaker to the Vin+. Supposedly I should receive ~5V at the output of the op amp. However, I can only receive ~2V (keep changing) even if I increase the voltage gain. What's wrong with it? Can I just cut the speaker off from the board and connect directly to the Vin+?