The invention relates to a device for alignment of a first component (1) and a second component (2) in a predetermined relation to each other, comprising a transmitter unit (7) arranged for mounting on said first component (1) and comprising a light source (9) for the generation of light radiation (10) with a predetermined pattern in the direction towards a receiver unit (11; 11′, 22, 27; 27′) arranged for mounting on said second component (2), where the receiver unit (11; 11′) comprises a detection device (18a, 18b; 18a′, 18b′ 23a, 23b; 28a, 28b; 28′a, 28′b) for said light radiation (10). The invention is characterised in that said detector device (18a, 18b; 18a′, 18b′, 23a, 23b; 28a, 28b, 28′a, 28′b) comprises a first detector (18a, 18a′ 23a; 28a; 28a′) and a second detector (18b; 18b′ 23b; 28b; 28′b), respectively, which are separated depthwise in relation to said transmitter unit (7). The invention also relates to a receiver unit (11; 11′; 22, 27, 27′) for the above-mentioned type of alignment, and also a method for such alignment. By means of the invention, an improved alignment of for example belt discs is provided.