There are a lot of reviews of this product, so let me impart the "Gravy" if you will.
1. The motion sensor works and has not had any false alarms ONCE we adjusted the sensitivity. At its least sensitive setting, the unit would alarm. Since adjusting to the "mid level" we have not had a single false alarm... However, if you pick up your kiddo in the middle of the night to change a full diaper, turn the unit off first or you'll wake up your sleeping spouse with the ALARM!
2. The sensing unit works fine in a crib without the masonite board. In the basonette, we used two towels on either side to "level" things out. The sensor still worked fine and the thin mattress pad was level.
3. The alarm is loud and will wake you up. Good.
4. The monitor microphone is sensitive and you can hear every little grunt, so we turn the volume down a little at night. A cry will be loud, grunts are not.
5. Our Uniden 5.4gHz phones do NOT interfere with the unit and it does not affect my wireless network.
Overall, we love the monitor.