Why do some hotel rooms install hidden cameras? what is the purpose?

Installing hidden cameras in hotel rooms is an invasion of guests! Suspected of breaking the law. This practice is actually using illegal means to spy and gain the privacy of guests. Therefore, when staying in the hotel, customers with strong awareness of prevention will turn off the lighting of the guest room, then turn on the camera function of the mobile phone and scan it with the camera lens of the mobile phone in order to find the hidden camera in time.