A sensor comprising a light emitter and light detector directly covered and encapsulated by a layer of light blocking compound. The light blocking compound can be thick enough between the light emitter and light detector to block substantially all light emitted by the light emitter from reaching the light detector directly, but be thin enough above the light emitter and light detector to allow at least some level of light emitted by the light emitter to escape out of the sensor, be reflected by another object, re-enter the sensor, and survive passing through the light blocking compound to enter the light detector.