Here's an idea for those doing this with a PIC or other micro. To add a bit of evilness, setup the PICs internal timer1 as a makeshift RTC and have it chirp at random intervals between 1 and 10 minutes. You could also choose a random frequency to drive a piezo speaker.
If it chirps with a predictable period, it is probably more likely that your device will be discovered.
Better make sure the victim has enough sense of humor so your poor electronic cricket doesn't get stepped on if he finds it-
That would be the advantage of the cheaper and less elaborate circuit, if it does get found, more disposable-
I've encountered real life crickets that would be a good model for what this should do- chirps away happily until you get close trying to find it, and then it stops, only to resume when you get tired of standing around waiting for more clues as to where it is, and walk away. Maddening.