Why do we have bells in the temple

According to ancient Hindu beliefs, by ringing a bell, the presence of a deity is evoked, which is believed to be extremely fruitful and rewarding. It also helps to reign in consciousness.
As per ancient Puranas, these bells are known to rid you of all the past sins. Scientifically, the vibration caused by these bells is quite high and is known to kill microbes and insects in its path. It keeps the temple premises clean and tidy.