What is the small hole in the exhaust fan of the hotel?

Sensor hole for detecting the running state of the fan. This sensor hole can monitor the running speed and rotating speed of the fan to ensure the normal operation of the fan, and can also be used to discharge the moisture and moisture accumulated inside the fan to keep the fan dry. Hotel exhaust fan is a kind of equipment used to exhaust the air inside the hotel, which is installed in kitchens, laundry rooms, bathrooms and other places where odor and moisture need to be exhausted.