Need help deciding how to sense speaker/radio activity

I am new to the Arduino world, and have a specific requirement I want to try to meet. My requirement here is to send when a signal is received by a radio and to count how many times a new signal is received in x seconds. The programming part of things is pretty straightforward I think, but the sensing part I am not sure how I can or should accomplish.

In more detail: If I have two walkie talkies, am transmitting with one and receiving with the other, I want to count how many quick transmissions are made in lets say 5 seconds. I am not going to speak on the radio, just keying the transmitter in quick succession x number of times and reliably sensing how many time in the time window the radio was keyed. Think of it as using the transmitting walkie talkie as a button and clicking it some number of times and the program keeping track of that and then deciding what to do based on the input.

So my questions is, how to best do this? I would think I maybe could set up a voltage sensor on the speaker of one walkie talkie, and loop to read that voltage from the sensor and look for a voltage to go high then increment the counter? Or would a software defined radio make more sense? Any other ideas or specific methods/circuits? I have the walkie talkie now, so if there's a way to reliably sense the "click" of each transmission on the speaker wires via voltage change or similar, that might be most accessible, but open to any ideas.

Thanks!

In order to offer any kind of help, you need to decide what type of radio you are going to use. Are you using FM walkie talkies or AM walkie talkies? If FM, they probably have a squelch circuit so there is no audio output until a carrier is received. You can access the squelch circuit to determine if the other walkie talkie has been keyed.

There are many different types of software defined radios. Pick one.

Paul