Both inside and outside have speaker and microphone, The volume and microphone sensitivity can be separately adjusted. Using a 4 core high-strength aluminum foil shielded wire , and strong connection plug. Microcomputer processing circuit solves the problem of and squeal. Have recording jack can be output both inside and outside the two-way voice signals (such as the bank teller system for recording). Can be used in any place which difficult to talk, such as bank, securities, hospital, bus station etc. Working voltage: DC12V / 500mA Adapter: 50/60Hz Main sound (sub sound): 5W+5W Microphone sensitivity: -46db±2 db(20Hz-16kHz) (The product appearance and printed words depending on the batch, but this does not affect use) Plug Type:US Plug,it applies to Canada, India,Mexico, Thailand, the , the Philippines,Taiwan and so on. Color: Black Material:ABS Package Contents: 1 x External speaker Only the above package content, other products are not included. Note: Light reflection and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.