I believe it to be a set point. I don't think the actual pressure is transmitted. The manual says they are triggered once the tire reachs a 10% loss in pressure. That equates 3.6 PSI on the SRT-6. I actually tried an experiment, and I "think" it worked. I put the tires up to 40 PSI and drove them for a day. I then dropped them back to 36 PSI (a 10% drop in pressure) and the light came on. So I then dropped the pressure to 32 PSI with the light remaining on for about an hour. I then put them back up to 36 PSI and the light went back off. It would seem that they "learn" based on what you set the pressure at above 36 PSI.