Unmanned self-propelled device (1) for carrying out activities in a space in which contaminants may occur, wherein the device comprises a frame and means for moving the device through the space, wherein the device further comprises a detector (20) for detecting a body in a detection range (22) of the detector, which detector is provided with an outer surface (21) which is exposed and which is permeable for the detection function, wherein the frame is provided with screening means (25) which are stationary with respect to said outer surface for keeping said outer surface free from contaminants, wherein the screening means are provided with at least one screening member (25) which is located in the detection range and has a first intercepting surface (25a) for intercepting contaminants moving towards the outer surface, wherein the detector has a detector centre line which intersects the outer surface, wherein the first intercepting surface, when viewed in at least one sectional plane which contains the detector centre line, extends along a line (F) which diverges with respect to the detector centre line in a direction away from the detector.
