Remember when Moss checked into the motel and stashed the valise in the heating duct? What tipped him off that there were guys waiting for him in his room, and how did those guys find him in the first place- Anton was the one with the homing devise. And how did Anton find him in the motel where he was killed? I guess I missed something. 
I don’t remember what tipped him off, but I do remember that the Mexicans had their own homing device, just like Anton did.
That being the case, you’d think for 2 million dollars they would have demolished that room down to the studs if they were in it and their devise was still beeping.
Perhaps they hadn’t been there long.
I vaguely recall a shot of the parking lot showing a vehicle and he took that as a clue that they were there.
They had their own homing device. But how did they know to go to Del Rio in the first place? I know that Anton saw (IIRC) a phone bill that tipped him off that Moss was going there, so he just went into that general direction and drove until the homing device started beeping.
Did they Mexicans also see that same phone bill or did they have other information to indicate that Moss would be going there?
That part of the movie involving the homing device seemed unrealistic to me. Wouldn’t it involve a lot of random driving around and blind luck to get close enough for the thing to start beeping? Maybe he just drove by every motel in town to see if it picked up the signal. Also, I really have no idea if that type of technology was realistic for the time period of the film. I’m sure someone else will know more about that than I do.