I cant' be of much help as I've never used any of these systems to discover overheated connections. The systems, like those provided by Omega, boast an accracy of about 1 degree C. This should be fine for line-of-sight instances. But for connections inside panels something like the glass covers mentioned by lynnbr2 might work.
Incidentally, the link to ElectroPhysics didn't mention anything about glass covers.
The thermal system explained by lynnbr2 is a good approach. There are inexpensive point and click systems that use a laser beam to determine the emissivity at a particular wavelength, and then a thermal sensor to measure the emission near that wavelength. These hand held systems are sold for consumers for use in kitchens for measuring the temperature of a pot, or a roast, or a pot roast... But when using a thermal approach one must have the circuit under significant power.
Great idea @lynnbr2. Anything that makes safety reviews and maintenance easier increases the likelihood that it will be performed. I like the idea of IR friendly glass which not only makes the checks easier, in many cases it means the checks do not require a process shutdown.
Focus on Fundamentals consists of 45-minute on-line classes that cover a host of technologies. You learn without leaving the comfort of your desk. All classes are taught by subject-matter experts and all are archived. So if you can't attend live, attend at your convenience.