• Most solutions use salt. Wikipedia, short article, About.com. Table salt soaked in a little bit of water in a closed container is 75% humidity regardless of temperature or pressure.

• Wireless Radar Scanning during Sleep or stationary. Way-cool radar scanning from Ted Punt and TNO. Radar can sense changes as small as 1mm!
  • Not sure on price
  • He said that you should be able to derive sleep quality from HRV and respiration. We'll see…
  • Amazing tech though, seems really hard, but he's a nice guy!
  • The other talks from QS Amsterdam
• That guy from MIT sensing heart rate from webcam.

* Good list of competitors from patent listing

• Zephyr Technologies BioHarness ($750)
  • Good battery life! Logged 11 hours w/ bluetooth disabled, and it used <25% of battery.
  • Records respiration and accelerometer too…
• Oregon Scientific WM100 Logger
  • Seems like a button cell battery SD card logger. $15 isn't bad…but it doesn't work with Coded straps, which might be more comfortable and no cross-talk
  • $8, but unsupported. Doesn't work with T31 coded chest strap. Coin cell battery seems to last for a long time though. Logs every 2 seconds and has memory for 30 hours.
• Garmin GPS logger is decent $140 No respir
  • Very in-depth review
  • Not sure how often it logs yet. It uses HRV data for Firstbeat, but that's as far as it goes…
  • Older models log more often?
• Suunto Watch Comparison
• Garmin Watch Comparison
• Open Source GPS and HR Logger

• MyBasis nice looking watch for $200 that logs HR, GSR, temp, and accelerometer!