Walmart offers the Trademark Driveway Patrol Infrared Wireless Home Security Alarm System for $16.26. (Amazon and Home Depot charge the same via free shipping and in-store pickup, respectively.) Choose in-store pickup to avoid the $5.99 shipping fee. That's tied with our September mention and the lowest price we could find now by $7. It includes a sensor and receiver and features a 400-foot range. Three C batteries and a 9-volt battery are required, not included.