There are chest-strap heart rate monitors which will work as long as you wear the strap (I think? I've never worn my for that long) and might work for 24 hours, if you can deal with having the strap on for that long a period of time. It might be uncomfortable for sleeping. I'd stick with what Kathy says for now - let us know what you find!
Female, 31 years old, 5'4 1/2" tall
Starting weight 1/4/11 = 215.2 lbs.
Weight 9/19/14 = 176.6 (net: -38.6)
Last mini-goal: 180 lbs. REACHED! Reward - new sports bra
Current min-goal: 175 lbs.
Next large goal: 165 lbs. by 12/25/2014
Lowest weight: 156.7 lbs.
150.2 lbs. <--- Official "Healthy BMI" weight
Estimated final goal: 130-140 lbs.
"You don't have to change your life today. You only need to change your day today."