This new style temperature probe will work with: Herpstat Intro, Herpstat 1 Basic, Herpstat 1, Herpstat 2, Herpstat 4, & Any Redline model. It also works with the following discontinued models: Herpstat ND, Herpstat II, & Herpstat Pro. Original model Herpstats with a serial number of 50102600 or greater. Original model Herpstats (front of unit is green and serial number starts with 5010xxxx) with a serial number between 50101000 and 50102600 require an older style probe that is no longer available. These units can be sent in and modified to work with our current temperature probes. Email firstname.lastname@example.org for details.