Phone and heart rate monitor?

littlewhittles

I don't know if this is the right place to ask this, but here goes. When I place my smartphone on the ledge of the elliptical at my gym, it makes the built-in heart rate monitor (the kind you grip to get readings on the machine) go crazy. Anyone else have any experience with this? It's not a big deal, I just can't get an accurate reading and thought it was weird.