This paper introduces a novel new smoke detector characterized by its very small size and very high sensitivity. The new detector is fundamentally based on an $alpha$-particle radiation source like the well-known $alpha$-particle smoke detector. However, instead of utilizing the principle of ionization of the air, the $alpha$ particles are made to strike the gate of an n-channel mosfet. This results in a net positive charge on the gate of the transistor. The current through the mosfet will be proportional to the charge on the gate and, hence, to the intensity of the $alpha$ particles. If particles of smoke enter the detector and screen the $alpha$ particles, the positive charge on the gate drops, which leads to a reduced current or total cut-off of the mosfet.