Dolly, the Tubby Test Card, is a specially designed tub temperature tester that features a built-in temperature strip. This device can be used alongside the elbow test to ensure water safety. If you're looking for an item hanging on a bathroom doorknob or tub spout, please look at item #TT15. No batteries or external power are required; the thermo strip detects the temperature and offers three easy-to-read temperature ranges. It's perfect for home use and pediatricians, preschools, & midwives.