If you want to know everything about your baby, down to the heartbeat — the Angelcare AC315 is our top motion-sensor monitor. The sensor mat slips under the mattress in your baby’s crib, and if it detects no movement after 20 seconds, it sends a loud alarm to the baby and parent units. Its touchscreen can be a little finicky. The Baby Delight is less prone to false alarms; however, our parent testers were concerned that the small clip-on sensor might be a choking hazard.
Dropped connections are another problem. "We tested our Wi-Fi monitors on two separate routers and consistently had problems -- we'd often lose the connection some time in the night and not even realize that the monitor had disconnected until morning," Wirecutter says. "This happened with all three Wi-Fi models we tested. We never really felt confident relying on any of the connected monitors overnight, despite the fact that the modem and router were literally on the other side of a wall from the monitor."