The PT Pro does not have a coded strap, so the CPU can pick up others' HR transmitters. I also think it is more apt to pick up interference from overhead electrical cables or electronic equipment.Mr. Finn said:I have a recentley purchased PT pro model. I am getting very unreliable Heart Rate readings from it. Seems accurate at the beggining then I look down and it will read 220 or somewhere near there. Any ideas on what could be causing this???