motion sensors are fun but I find that a low tech trick works for me. I take 25 or 20 pound test olive colored fishing line and tie one end to a branch of a bush and run it along the ground across a trail and tie the other end to a tree or an immovable object. I than set up an ambush position behind the string. When players come by they trip the wire and it moves the bush and they immediatly face the source of movement and fire or freeze this makes it easier to acuire my shots and take them out. The fishing line will break though if somebody runs into so it is safe. I have never had anybody hurt but there sure have been quite a few eliminated with this simple trick.