Clean

Remove the detector cover by snooping away the four sides tabs using a flat screw driver and then pulling the cover from the base.
Remove the protective screen by pulling it straight out.
Carefully vacuum the chamber and screen. If there is stain, wash with running water and ensure it is completely dry.
Position the chamber and screen by aligning three tiny holes over the sensing component.
Align the LED tube and tabs and gently pushing the cover until it locks into place.
Re-install and test the detector.