Hagen Exo Terra LED Rept O Meter Hygrometer with Probe. The Exo Terra Digital Thermometer and Hygrometer are each equipped with a remote sensor for accurate measurement and durability. These precise instruments can be programmed with a minimum and maximum memory setting. The sensor is held in place with a suction cup, and the instrument can be mounted either with velcro, with a screw or it simply slides into place on a new Exo Terra Compact Top or Dual Top.