Can anyone tell me where the wires go on a connected mains powers smoke alarm , one upstairs is ok but when i took the one in the hall down some wires came loose , one cable has a red,blue,yellow and earth and the other has red,black, and Earth, and the cable on the alarm has blue,brown and white . Where do I connect all to the block, cheers

Difficult to tell. The red, black and earth are going to be the live and neutral plus earth which comes from the lighting circuit/consumer unit to power the alarms. The three core (Red, blue, yellow) will be live , neutral and interconnect, but not necessarily in that order.

My guess is the upstairs one is linked from the downstairs one. Take the cover off that and you will probably see red, blue, yellow. If the alarms are the same then the connections should be labelled and just repeat downstairs, with the red and black from the 2 core going into the Live and neutral respectively.

Post pictures of them both and I should be able to identify it.

Rich.

Identifying mains cabling based on colour is a really, really bad idea.

I’d want to put a meter across them (after making very certain that it was isolated from the supply).

IANAelectrician.

Thanks for your response guys , the upstairs has 2 red and a black going into it , struggling to upload photos at moment