The Alpha Communications / S.T.R.™ TT33-3 QwikBUS Panel Speaker/Microphone units are used with the S.T.R.™ QwikBUS™ systems to provide intercom functions at remote door entry locations, and depending on system configuration, optional electric door opener(s) etc.The TT33-3 powers from the associated model# SP333 QwikBUS™ Intelligent Controller unit(s), and does not require any additional power supply unit(s). When used with conventional pushbutton type door entry stations where electric door release is required, the TT33-3 will also require a model# T1240 U.L. Listed 12VAC plug-in transformer.The TT33-3 speaker/microphones are designed to easily mount right behind the faceplate in various models of our lobby entry pushbutton style intercom panels.The TT33-3 speaker/microphones also feature a built-in door release relay, voice volume control potentiometer and a plug-in connector for connection to the model# E32 32 station 2-wire extender(s).The PC boards are treated with a special chemical finish, to minimize the affects of weather and moisture on the electronic components