Where do I obtain replacement DL09 and DL010 sensor detectors supplied originally by Smiths Industries Environmental Controls Company Ltd?

The company is now 'Timeguard', but operates from the same premises. The range on offer is much altered, but they may be able to help if another company took over that part of Smiths, unlikely as it is. It would help to know that the DL09 and DL010 are, how they are used, and what they do.