[Altor]

I too have used a whistle on a unwanted caller. I was getting a rash of "Windows support" calls trying to tell me my computer was infected. When I'm bored, I'll play along for a few minutes before I tell the guy to stop scamming people and get a real job. A couple of times, I happened to have my whistle near the phone. I let him have it.

As so_cal_lurker suggested, I wouldn't use it on a true telemarketer or somebody soliciting legitimate donations. But, these guys are scum who prey on the elderly and the naive.