There is a known issue with this product: the microphone socket is missing.

Using this Clear - Com RM - 400A remote station is straightforward. First, connect it to your relevant system as per the standard connection methods. However, keep in mind that the microphone socket is missing, so you can't use a microphone directly with it. For maintenance, keep it in a dry and clean place to avoid any damage to its internal components. Don't expose it to extreme temperatures or humidity as it may affect its performance. If you plan to use a microphone, you'll need to find an alternative way to connect it.