the buzzer starts buzzing faster and faster when they get closer to their objective.
That would make things too easy, I would think. You walk in a little circle and see which direction gets you closest and go that way.
Besides, if it would work with GPS that would make it quite complex. Measuring the delays of radio responses is similarly tough (radio moves at 1 foot per nanosec, necessitating a 1GHz counter, the electronics for which is a specialty art in itself).
The one doing the pressing gets an immediate distance clue due to the slow speed of sound.
The speed of sound is about 340 meters/sec, so the delay between when you press and when you hear is a very observable, and if you're good, quantifiable one second.
When you're 100m away the delay is only a third of second, quite noticeably quicker.
Volume wise it would also sound like it's about 300m away, especially if one has heard the beep up close first to guage the volume attenuation.
Also, if you happen to be approximately facing the sound, your two ears would give your brain a pretty good clue of the direction.
The low to high frequency squeal-like sweep is helpful because different pitches have different directional and reflective effects.
In the woods, or other rough terrain, if you used only one frequency beep, it might get confusing since that beep would reflect off rocks, trees, buildings, etc.
Maybe you want it not to be too easy, and pitch sweep is an adjustment.
A changing frequency is more comprensive, reflecting differently on different objects. I think bats, dolphins, and whales all use some type of squeal.