1byone via Amazon offers Prime members the 1byone Door Stopper Alarm with Built-in Alert System, model no. 100US-0001, for $7.99 with free shipping. (Non-members can spend $35 or more to qualify for free shipping; otherwise, shipping costs $6.63.) That's tied with our November mention (which required a coupon) at $9 off and the lowest total price we could find. It features a motion sensor function and compatibility with all 1byone alarm receivers. Deal ends March 28.