Wraith scanner
From The Stargate Omnipedia
Portable device worn on the left forearm of Wraith hunters. Remarkably similar in design to Ancient scanners (perhaps not so coincidentally), the device displays life signs in the form of flashing blips, distinguishing the wearer from his prey.
KEY EPISODE
Sateda - Multiple Wraith arm themselves with scanners to detect Ronon on the surface of his home world, but the soldiers soon learn that sophisticated technology cannot help an unprepared hunter.