Here is an example of a fully submersible high temperature datalogger. Because it will function under pressure and at temperatures well above 212F; it can be used for monitoring and verification of high temperature processes such as low acid canning. For example, in low acid canning a retort or pressure canner will get to 10-15 psi and 240-250F. Unfortunately, this datalogger in the high temperature model will run $400-$500 dollars. The photo model is “deltatrak“, but there are other brands available.