1. A monitoring device for vehicles, said monitoring device comprising: a housing ( 17 ); at least one mirror glass ( 1, 12 ) arranged in said housing ( 17 ) so as to have a front side facing an observer; said at least one mirror glass ( 1, 12 ) comprising a reflective layer ( 5 ) being reflective in the visible spectral range of light; at least one camera ( 10 ) arranged behind said reflective layer ( 5 ) in a viewing direction viewed from said front side.