Abstract: A toner cartridge is modified by the addition of a low toner sensing mechanism internal to the cartridge. An arm is pivotably mounted within the cartridge; the suspended end of the arm having a magnet secured thereto. When the cartridge is filled to a relatively high level with toner and rotated, the suspended arm is at least partially submerged in the toner bed and is subjected to a viscous drag force which moves the arm from the vertical position and prevents the arm from returning to the vertical or plumb orientation until a sufficiently low toner level occurs. At this point the arm is sufficiently free from the viscous drag effects of the rotating toner bed and attains a plumb position which brings it into alignment with a switching circuit which is closed by action of the proximate magnet. The switching circuitry generates signals which are used to produce a visible or audible signal to the operator, and/or which cause machine shut down to occur.