ST4 WiFi Thermometer Freezer Alarm, Email Alert, App Notification, Data Record Export, No Subscription Fee, Remote Wireless Temperature Sensor for Refrigerator, Freezer, Hot Tub (2 Pack) 4.3 out of 5 stars 429. 1K+ bought in past month ... Pond Water Temperature Thermometer for Hot Tub,Spa. 3.9 out of 5 stars 233. 2K+ bought in past month. $39. ...