There is a serial Bluetooth module that I have used before on an Arduino project but now I'm trying to use in a project without the Arduino. Basically I need it to be an electronic trigger, I don't care really what the signal is just how long and the voltage and current. There are 4 pins on the module: Vcc, GND, Tx, and Rx. There are 2 open pads: Key and State. When I send a command from my phone the module sends a signal out the Tx pin, and it is this signal I would like to measure so I can pick a command with an appropriate signal and tailor the rest of the circuit accordingly. I tried a voltmeter between Tx and GND but saw no signal on any level measuring DC. Is there something I'm missing? Is the signal more complex or different, or is that test setup flawed? I tried other combinations, Rx-GND, Tx-Rx, RX-Tx, GND-Tx, GND-Rx but saw nothing.