An assistive listening device, or A-L-D, differs from a regular hearing aid in a number of ways. The simplest ones consist of an ear mold which fits inside the ear. Two wires are attached to it. One of these is connected to a small box that can be worn inside a shirt or pocket. The other wire connects to a microphone which can be placed near the sound source so you can hear what is being said without interference from background noise. These A-L-Ds are particularly handy for home use. Other, more sophisticated versions utilize electronic signals rather than the box and microphone. They are useful in large rooms or groups. To determine the nature and extent of your hearing loss, have your hearing checked by a specialist. If an A-L-D or hearing aid is called for, an ear specialist will be able to advise you as to which type will be best for you. Size or type should be determined by the nature of your hearing problem. Bone conductors are worn against the skull. For air conductors, a mold is made to 'fit' into the external auditory canal.