Assistive Listening Devices have come a long way.
Modern technology has provided a multitude of alerting devices for people with impaired hearing. The most popular technologies now available for a wake up alarm, a knock at the door or a smoke detector are one of three types: vibration, flashing or strobe lights, and audible sound systems.
What works best for you is a highly personal choice. Some prefer the silent signal of vibrations. The more powerful vibrating wake-up devices are called bed shakers and the smaller types are known as pillow shakers. There are also vibrating wristwatches.
Flashing signalers also have a range of devices that work well. Flashing incandescent lamps are very popular. Others say only a strobe will work, because it produces a high degree of intense light. Again this is a matter of personal choice, though flashing lights can produce other problems - for example when people are epileptic.
Also in the running for most useful and popular wake-up alerting devices are those that produce loud audible signals. A good audible alerting device will have separate volume and tone controls. Of course, these products are for the hard of hearing, rather than the totally deaf. They also have the drawback of possibly disturbing others in the vicinity who are not hard of hearing.
Here's a helpful breakdown on the features of the three different types of alerting devices:
Vibration Alert: There are some bed shakers that alert you by a continuous single-phase vibration. This means it produces a steady vibration until you either shut it off or it turns itself off. Another type of vibrator alerts you by emitting a pulse-style vibration. This is an on/off, on/off type of alert. It releases a burst of vibration, stops, then vibrates again. It will continue to vibrate until it is deactivated.
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