I think they will fit one if you qualify, i.e OAP etc
Breezer,
They may not be what the OP wanted but you don't have to be a pensioner to get them.
I'm not a pensioner yet but they fitted two for us.
They offer a free home and fire safety inspection to anyone and will install as many battery powered smoke alarms as the premises need, all with ten year batteries.
They just said to call them when the low battery warning started beeping and they will be round to replace the unit.
I only suggested it as an alternative to running wires everywhere.
dave