An alerting device is a device which helps people with hearing problems. It doesn’t only help deaf people, it helps people with any kind of hearing problem. Alerting device, in medical terms, is also called Assistive Listening Device. The way it works, is that it eliminates all of the background noise and makes the sound clear, therefore easier for a person to hear. Many public places nowadays, such as churches, theaters offer these hearing aids for people with these kind of disabilities.Beside these devices, which are made for deaf people all the time, there are several other device which help in hearing better. Some of these are: alarm clock, baby crier, door knocker, fire alarm, phone flasher, vibrator etc. Such alarm clocks are special made for deaf people, they are very loud. You can choose a frequency which you hear best, there are options for flashing light, vibrating etc. A baby crier is a device which helps you hear when a baby is crying. It vibrates and light flashes. Door knocker works with the same principle. When someone knocks at the door, a device vibrates and flashes lights, so that a person with hearing problems knows that someone is at the door.The same principle is with the other terms.