Messey, TR were what their name implies but they were quite big in fire alarms right up until the late 1970s or early 1980s. They used to rent fire alarm systems over a long period, like a finance lease almost. In the 1970s as I recall they used Nittan detectors. The detector you describe is almost certainly the old Chubb rate of rise/fixed temperature heat detector, which operated on the principle of two bimetallic strips. (Ask any of the older fire safety officers in your particular FRS. Since they dont do any CPD they will probably think thats still how all heat detectors operate.) The detector was invented in the 1960s and was hailed to be state of the art technology. It was used right through the 1970s and even into the 1980s. There are still many around and they continue to operate effectively. They have the unfortunate feature of a resonant frequency (although not at a frequency used to test detectors for normal land applications) at which the bimetallic strips vibrate with excessive amplitude causing false alarms, making them unsuitable for high vibration areas on ships, but otherwise they were an excellent detector that successfully detected many fires which the greatest fire brigade in the whole of...... London no doubt extinguished with equal efficiency and 50 appliances per fire.
