The TS-901 is a Chairman unit of the Infrared Conference system. Since the system is cordless, it can be easily installed and removed. The Chairman unit features a priority speech key which allows it to take precedence over the TS-902 Delegate units ( optional) when speaking. It can be operated on either the AD-0910 AC adapter ( optional) or the BP-900 lithium-ion battery ( optional) . It is equipped with a remaining battery indicator. Two types of dedicated microphones are made available for the TS-901 as optional products: the TS-903 standard type and the TS-904 long typ