Help identifying this electrical device

This is in my hallway behind a blank plate.

Front & Back Images

The front of it seems to be painted over so the only identifying marks are on the back side. There are four terminals labeled "R", "Y", "GR", and "BK". The GR terminal is not connected. There is also a code "493A" which I assume refers to the model # of the device but searching has not been helpful.

Is anyone familiar with what this would be?

Edit: After searching up the 4-Prong telephone connector, that's exactly what this is. Thank you everyone who took time to answer!