Checking the status of the eruv immediately before the Sabbath begins will avoid most violations. Some people don't bother to check and make the (IMHO, safe) assumption that the eruv is intact. Some people don't bother to check and make the (IMHO, rather inconvenient) assumption that the eruv isn't intact. In particular, this involves some sort of alternate plan for getting back into your house. Some people "wear" their keys. I think some people distinguish between different categories of carryable objects based on their necessity. The eruv is not something that I'm personally involved with so I'm not very knowledgable and the only thing that I can really say with confidence is that it's a thousand times more complex than anything I could hope to explain here.

Cleveland's eruv status is available by phone (as is the East London, I believe; also, I think, the prefered method) and on the web site of the local Jewish paper as text (unknown as of 11AM).