I have a polar heart rate monitor.
I can't recall the model, but it certainly wasn't the top line model.
It has a chest strap, and you wear the monitor like a watch, and the chest strap sends signals to the "watch" and it displays your current heart rate, and also shows maximum, minimum, average etc.
I wear it swimming, free weights, body combat, spin cycle, running, whatever, wherever.
The only problem I had was in the month or so after surgery my chest scar caused some discomfort with the chest starp, so I didn't wear it then, but its fine now.
I bought it on line a couple of years ago, and it was about $120 dollars australian...(I think that now equates to about $1,500 dollars US....just joking ...just joking....I remember the time when $1 Australian was only worth 45 US cents....but boy, the USD has taken a battering over recent times)
Anyway, I love it, and for me it was the key to my fitness and weight loss....honestly, it made a world of difference.
I was walking and walking, and exercising, thinking I was doing a reasonable job, but I found out that my heart rate was just staying that little bit too slow to be doing me much good, so when I got the monitor, and the exercise physiologist gave me a target heart rate to try and achieve during exercise (based on my age and weight etc), I improved out of sight...honestly.
Anyway, see how you go tracking down a polar heart rate monitor. I totally agree with Steve Epstein, and I highly recommend it.