Best Buy offers the PEQ 3-Series Contact Sensor, model no. 3300-P, for $9.49 plus $5.49 for shipping. That's $5 under our mention from last November and the lowest total price we've seen. (It's also a current low by $9.) Designed for use with most ZigBee HA 1.2-compatible platforms, it detects the opening and closing of doors and windows and includes all mounting hardware.