Abstract: A device for measuring the particle content of air comprises a laser source for generating laser light and for directing it to a target area, an air channel for directing the air subjected to the measurement as an air flow through the target area, and a light detector located adjacent to the target area for detecting bursts of light generated as the particles entrained with the air flow scatter the laser light in the target area. The device comprises a light trap between the laser source and the target area for reducing stray light propagating to the target area. The light trap comprises at least two intermediate walls which are substantially transverse in relation to the propagation direction of the laser light, each of the intermediate walls having an aperture for passage of a desirably limited amount of the laser light through the given intermediate wall. The intermediate walls are part of a same piece manufactured as one continuous block.

Abstract: Procedure for providing an answering service in a telecommunications network (1), which comprises a first short-message service center (2); a telephone network (3) using digital signalling and connected to the mobile communication network and a number of telecommunication terminals (4; 41, 42, . . . , 4n), which are compatible with the mobile communication and/or telephone network, in which procedure a response message is transmitted from a called party's telecommunications terminal to a calling party's telecommunication terminal after the calling party has tried to call the called party, who has activated an answering service in his/her telecommunication terminal. According to the invention, the response message is a predetermined short message. The telephone netowrk (3) isi connected to the first short-message service center (2) via a first telecommunication link (6).