EBay's money back guarantee only for 30 days after delivery. After that, they will not get involved, whatever the problem.
PayPal buyer protection lasts longer, for 180 days, but only covers faults present on delivery. Neither will get involved in warranties or faults that occur in use.
Responsibility now rests entitely with the seller. If they're a UK business seller, you can consult trading standards or citizens advice.
You never know where eBay sellers get thier stock, and when things go wrong many don't know or want to know about their responsibilities. As you now realise, eBay itself won't give the buyer any help of support after 30 days. These are all reasons to think twice before buying through eBay, especially for anything safety-critical like a smoke alarm.
