Indoor phone Technical Parameter a) Working voltage: DC 18V?0% b) Static current: ≤35mA c) Working current: ≤500mA d) Kinescope: 4" flat tube(black/white) e) Color display: 4"color LCD display Resolution: less than 450 points. f) Environmental Temperature: -10 to +55 degrees g) Humidity: 45% to 95%