Nest smoke alarm wiring advice

[Alpha1]

I'm looking to wire in a Nest smoke alarm, the current hard wired smoke alarm is using the lighting circuit for power. I have taken it off the ceiling and the photo of the wiring is below.

The only thing I am confused about is the yellow wire with the red sleeve. I understand all the others, but this one is a bit confusing, I think it might be the communication wire to the other smoke alarm (given that it's white on the other side of the terminal connector) however the red sleeving worries me a bit as normally that would indicate the switch live, any ideas from PH on this?

[Contract Killer]

Correct.

[Alpha1]

Thanks mate, all installed and working.