Harbor Freight sells outdoor motion sensors with indoor alarms for not much money. Their normal price is $15.99 but they often have coupons that allow you to buy them for $8.99 or $9.99. They sell three different models for the same price which all look identical. The only one that I know that the RFXtrx433 will detect is item 93068. I’ve been unable to get either item 61910 or item 62447 to be detected by the transceiver. Also, I can’t yet comment on the working distance of the 93068 or it’s weather-proofing, although it looks well sealed.