The Golden Rod Wireless Hygrometer was designed to display the humidity in your vault without ever opening it. The wireless LCD display clearly shows the in-vault and in-room humidity and temperature levels through its remote sensor. Simply place the sensor in your vault and put the display screen anywhere convienent with its built in kick stand support or magnetic back. The Hygrometer measures and displays humidity from 20% to 90% while also recording minimum and maximum records. This battery operated Hygrometer is a must have for every vault owner. It uses 4x AAA batteries (2x in the display, and 2x in the sensor), batteries are included.