What is one of the types of alerting devices for the deaf and hard of hearing?

A hearing dog is indeed a type of alerting device for the deaf and hard of hearing. These specially trained dogs are used for a variety of alerting purposes such as notifying their owners of sounds like door knocks, alarms, or calls on the phone. They provide companionship and assist their handlers in important ways, enhancing independence and safety in daily life.

The other options listed serve different functions related to hearing assistance. A telecoil is used to connect hearing aids directly to hearing loops in public spaces, allowing for clearer sound. A directional microphone enhances sound pickup from a specific direction while minimizing ambient noise, and an FM system provides direct audio input through radio frequencies, often used in educational settings. However, none of these devices play the specific role of alerting individuals to environmental sounds in the same way that a hearing dog does.