According to this page on the website of a company named “Applied Fire Technologies, LLC”, Masterguard, supposedly a brand name/“sub-brand” of the Gentex Corporation that they sold smoke detectors, heat detectors, CO detectors, & fire extinguishers to residential consumers with, is no more. When exactly is unknown, but going by the fact that Gentex discontinued the last smoke detectors that Masterguard were selling a year ago or so, it’s likely recent. As that page says Applied Fire has taken over customer service for the Masterguard brand & had masterguard.com redirect to that page on their website (the latter of which is more evidence that Masterguard is gone as I know it still worked only some years back). I also believe that Applied Fire was once a “customer” of Masterguard (or rather Sure Signal Products, the supposed original maker of those wind-up heat detectors) so-to-speak as they sold/sell a version of Masterguard’s QR50 heat detector (along with several other companies as this page shows: “ThermaLINK” was/is Applied’s model), so I guess it would make sense that they would “take over operations” for what’s left of Masterguard.
We bought the heat sensor alarms back in the 80’s. We’ve taken them from house to house because the saved us when the wood stove got so hot the wall on other side was too hot to touch. Anyway we just moved again and we are missing a bracket for one and the heat seal disc. Can we still get them and are they still good to use?
They might still work, but likely good luck trying to get new fuses for them as they might not be made anymore.