Best outdoor motion sensor?

No such thing as best performance and lowest cost good units run $150+ and into several hundred dollars if you want a unit that covers and does not false and it also requires keeping weeds cut down etc.

Honeywell has a pretty good one

5800PIR-OD

Check on line. They are (relatively not inexpensive) Anyplace that I would recommend to you would only sell to installing dealers.

I've had success with both of these but out door motion detectors ..... are designed to detect ... yep, you guessed it ... Motion. Don't get your hopes too high that it will only detect the motion that "you" want it to detect. There are some dual technology products out there along with photoelectric and even Microwave that are more than twice a good, but they definitely don't fall into the "inexpensive" category.

Also very steady and reliable is Texecom's external TD

best one I have found is the Bosch OD 850 series. Use that part number and search online for the best deal. There was a guy that posted here for years and promised to sell alarm gear at a good price but he is pushing daisies now. I would mention the name but few here seem to miss his demise.