Some models also allow the user to switch the ring to a different pitch in case their hearing loss is at the same pitch as the standard telephone ring. This causes a light to flash whenever the telephone rings. Some units have flashing lights built in, others allow you to plug in a lamp or other device that will flash. Voice Amplifiers - Some attach to the telephone line and others are built right into the handset or phone. They have an adjustable volume control that will make the callers voice louder.
Some models are portable and can be used when traveling.
These devices allow a person to plug a regular telephone into a small keyboard that has a small screen. When a TTY calls another TTY, the users can communicate by typing what they want to say and the words will be displayed on the other persons machine. Some even allow the conversation to be printed for later review. Sensors can be used to detect the doorbell, telephone, fire alarm, a baby's cry, or any other sound. The sensor then sends a signal to a receiver which may sound a loud horn or bell, flash lights, or activate a device to vibrate the bed.