A terrarium with a working heat gradient has a warm end and a cool end by design, and guessing at that gradient by feel is a poor substitute for actually reading it in two places.

Exo Terra's analog Thermometer is self-adhesive: peel off the paper backing, make sure the surface is clean and dry, and press it on. It can be used on its own in a central location for a general reading, or in pairs — one unit at the warmest spot and one at the coolest — to properly track the gradient, and it's best kept away from direct light or heat from incandescent bulbs, which can skew the reading.

• Self-adhesive backing for surface mounting
• Easy-to-read analog display
• Usable singly (central placement) or in pairs (warm spot and cool spot)
• Keep away from direct light or heat from incandescent bulbs

One thing worth knowing. No temperature range or accuracy figure is published for this thermometer, so treat the reading as a general guide rather than a precise measurement, and Exo Terra don't state how long the adhesive holds before it may need repositioning.

Who it's for: keepers who want a simple, visual way to confirm they've actually got a temperature gradient across the tank, not just a single spot reading.