In order to sense the voltage on the phone line, the unit’s circuitry must draw a small amount of current from the phone line. The current draw is very small (70 μA, similar to a voltmeter), and is drawn when the phone line is On Hook. The telephone company’s amplifier supplying the power to your location may not be able to supply this current and still keep the On Hook voltage level within the standard range. This occurs primarily in older residential and commercial locations. An unsophisticated telephone company repair technician may diagnose this small current draw by the unit as a “short” on the line. Therefore, the telephone company will not address the shortcoming of their supply amplifier. If this situation occurs, the unit cannot be used in the voltage detection mode, it must be reconfigured to the current detection mode.