Something more expensive, but I think more versatile, might be the MURS Alert™ Transmitter
and one of their M538-HT handheld transceivers
. Dakota Alert even calls it "a revolutionary new trail monitoring system."
You could have up to four of the MATs on one channel, each with a different alert code, so you'd know from which direction something or someone was approaching. The range on them isn't real big, but on a mobile receiver with an external antenna, I've been able to hear one of my MATs transmitting from over a mile-and-a-half away.
I don't remember getting an "ear bud" with either of my handheld transceivers, but Cabelas mentions it on their site. (They don't carry the radios anymore.) With the ear bud, you could monitor the MAT(s) without the receiver squawking or blaring out a chiming sound when something crossed in front of the PIR. (I've got a slightly different driveway alert, and it only has two volume settings. Even the lower setting is probably louder than you'd want to have up in a tree stand with you. "♫ DING DONG!
" And Bucky's headed the other direction.)
Just a thought.