Generally speaking, signal generators trigger an audible or visual function when they receive an electronic current. In cases where an alarm might need to come on following a sensor detecting something, for example a temperature indicator, a signalling product is ideal for the job. There are three main kinds: acoustic signal generation products, optical signal generators and devices that offer a combination of the two. Audio signal processors offer sound generation by a number of means. Some are simple loudspeakers that can be fitted into an electrical product virtually anywhere, and wired to a remote circuit board. Others are designed for direct mounting onto a PCB, and these sorts of small signalling devices tend to offer piezo-level sounds. In addition, horns and sirens can operate as acoustic signal generators and these are often suited to industrial installations. Where the generator rings a bell, the use is often for emergency building evacuation notification. Optical signal generating products include flashing beacons and warning lights, such as those that might be installed in an industrial user console. Some of these devices rotate in order to offer a comprehensive warning system, especially when they are combined with sound generation. Various accessories, such as incandescent lamps and mounting brackets, also fall into this product category.