One of my readers is always concerned about the availability of some components used in my circuits. Even though new makes are releasing continuously, the old makes are still in the market. Indian electronics market is rich in new as well as old components and the old one cannot be considered as obsolete. Substitutes are also easily available. We cannot argue if the component is not available in one country since the availability and use varies in different regions. A wise designer can easily substitute a component if the make shown in the circuit is not available.
This simple circuit acts as a warning device whenever the temperature exceeds the preset level in its vicinity. It is an ideal circuit to monitor the heat generating devices like PC, Inverter etc.