In an effort to keep control of the raging Hulk inside him, Bruce Banner (Edward Norton) used a heart rate monitor to stay aware of his body and prevent his metamorphosis into the jade giant. Production noted this as one of the monitors used by actor Edward Norton that was given to him by Betty Ross (Liv Tyler).
This is an actual POLAR brand heart monitor watch. Made from a charcoal and grey rubber band with metal clasp item features a square face and measures 10" long. Item is mint, untested but presumably in working condition (just dead batteries). Screen is not scratched, that's just a reflection of something in front of it.
COA: Marvel Studios