The statement "One type of personal health monitor measures the amount of time you spend in REM sleep." is **True**.
1. **Explanation**:
- REM (Rapid Eye Movement) sleep is a stage of sleep where most dreaming occurs.
- Some advanced personal health monitors or trackers, like certain smartwatches or sleep tracking devices, can analyze your sleep patterns and stages.
- These devices use sensors to detect movements and other data to estimate the time spent in each sleep stage, including REM sleep.
- By monitoring REM sleep, individuals can gain insights into their sleep quality, patterns, and overall health.
Therefore, a personal health monitor that measures the time spent in REM sleep is a valid and accurate feature in some devices, making the statement **True**.
