So that beeping started and sure enough it was 3am – the first sign that my smoke detectors needed a new battery, so I thought. On further inspection it appears that they were starting to malfunction. I went on line an took a look at the cost to replace the whole lot with similar detectors that would work with the existing wiring. I found the replacements and sure enough they are really easy to take the old one off and replace it with a very similar one. We replaced 6 of them all for about $70 – Not too bad to provide safety devices for the whole family in case of a fire.