Just for what its worth dept:
"If smoke alarms in your home are more than ten years old, NFPA recommends replacing them as well.
Why? According to NFPA, aging smoke alarms don't operate as efficiently and are often the source for nuisance alarms. Older smoke alarms are estimated to have a 30% probability of failure within the first ten years. Newer smoke alarms do better, but should be replaced after ten years. Unless you know that the smoke alarms are new, replacing them when moving into a new residence is also recommended by NFPA."
I clipped this from an Internet site. I would assume that it is probably applicable for detectors in our Airstreams also.
'04 Classic 30' S.O.,'03 GMC Savana 2500,'08 Vespa GTS 250