It comes with one receiver and two thermometer sensors. You can add another two sensors to monitor up to four fish tanks. I purchased these for my salt water tanks but I changed my plan. It is very accurate thermometer and cost me $60.00 new online and I am selling for $25.00 Firm. They are only less than 4 months old, I even still have the box. They run on battery, very nice units. Pick up only in Yorba Linda, California. Serious buyer, email me with phone number at babybetta@earthlink.net
