Flagging noteworthy moments during lengthy video recording? I work in a developmental psychology lab where it would be useful to have audio / video documentation of notable behavior and speech patterns.  Sessions with subjects last for several hours, and during this time, most of my attention is devoted to the proper administration of tests.  It would be nice to have something as simple as a button press that inserts some type of marker / flag / bookmark / chapter division into the video footage whenever I observe noteworthy behavior I'll want to review later on.  During review, I envision being able to use the marker system to jump straight to these moments of interest.

The chief issue I'm trying to avoid here is wasting a bunch of time searching through hours of tape just to collect a few minutes (or even seconds) of worthwhile footage.

I realize that a low-tech workaround would be to just synchronize a stopwatch to the start of the tape, and just glance at this / jot down times whenever anything interesting happens.  However, this would still be a somewhat cumbersome undertaking, as I also use a stopwatch during the administration of several tests.  

Is anybody familiar with any specific camcorders that could handle this sort of thing?  Perhaps a model that lets you insert "chapter breaks" while recording?  Any input is appreciated - I feel I may be missing some other obvious ideas here.

P.S.  Ideally, my "button" would actually be a foot-pedal beneath the testing table, which would, in some way, communicate with the camcorder - but I'd be plenty satisfied if I could accomplish this via some button operation on the camcorder itself.
If the camcorder records stereo sound and you are only interested in mono recordings, the foot switch could trigger an oscillator that injected a short tone on the left channel and the inverted tone on the right channel. 

During regular playback where you might be mixing left and right audio to one mono audio signal, the tone will be unheard because of electrical cancellation of the signals. However, if you had a small electronic circuit that looked for the presence of the tone on (say) the right channel then it would find it.

A better version would use a balanced differential amplifier to look at both left and right together - pure mono sounds (i.e. the sounds you collected in your recording) would be totally cancelled by the differential mixing in the amplifier whereas the "tone" you injected would be plainly and unambiguously heard reminding you to play back the regular recording at this point.