Spec Sheet Preview: The Alpha Communications® / TekTone OH20_ flush series backbox / housings are made of heavy gauge galvanized steel. They are designed to be used with the OF20_ series aluminum panel and master annunciator frames. These backboxes / housings are used with a variety of apartment entry intercom and video intercom lobby panel modules, as well as nurse-call, emergency-call and specialty master annunciator modules. The OH20_ series flush backbox / housing is open at the back of housing, to allow for wire entry. …