Although the frequency "Tiny Cooling Fan" has a high reliability, but it is still mechanical devices, in the long-term use, the speed may drop even stopped, so it is best for the fans running real-time monitoring, to facilitate the timely find the problem. At present, the fan's own alarm monitoring methods and the speed sensor are two types of alarm sensors can use an alarm signal in the "Tiny Cooling Fan" speed falls below a certain threshold value, and fan speed signal output can be realized Real-time monitoring of speeds. "Tiny Cooling Fan" circuit outputs an alarm signal from the "high" and "low" states, meaning two levels represented by the general system in accordance with positive logic, high indicates "failure", " low "for" normal. "