In one example in accordance with the present disclosure a drop detection device is described. The device includes an emitter member having a number of emitter cavities to relay a number of beams towards a number of detector cavities in a detector member. The device also includes a detector member that is spaced from the emitter member. The detector member includes a number of detector cavities to receive a number of beams from the number of emitter cavities. The device also includes a number of ribs coupled to both the emitter member and the detector member. The number of ribs space and align the emitter member and detector member and align the number of emitter cavities with the corresponding number of detector cavities.