The "To Keep Up" Wiki

Amazon listing Vauno EN8822C-1Hygrometer Humidity Gauge Meter - Wireless Indoor Outdoor Thermometer with 1 Remote Sensor - Room Thermometer for Home, Temperature and Humidity Monitor for Greenhouse Nursery Garden, 200ft/60m Range Listed $16.99 with $3 coupon
4 AAA batteries required (2 each base station and remote sensor)
Handles up to 3 remote sensors (one comes with unit)

1. Gather the needed AAA batteries, 2 for base and 2 for remote.
2. Remove old batteries.
3. Wait a few seconds.
4. Insert new batteries, pay attention to orientation
5. Resync if necessary.
   1. Press TX button on sensor

You should see the remote temperature displaying.