On Nov 11, 3:36*pm, "john east" wrote:
Have an ordinary house smoke alarm. *It's about twenty years old and it has
recently gone off in the middle of the night for two days running and for no
apparent reason.

I've heard that it might need a vacuum cleaner applied to it. *Is there
likely any truth in that, or is there anything else i might usefully do?

Or does it probably mean that I have to replace it?

There has been some discussion here before, based on half-lives, as to
whether the expiry date is absolute, or just a guideline for people
who don't test them. Mine are 20 years old and still detect my burning
the toast, so I suppose they're OK. They do beep when the battery is
low. This is exacerbated by lower temperatures, as when the heating
goes off at night. Was the "false alarm" just a slow series of low-
battery beeps or a full-blown screech?

Chris