The following text is an extract from the Menvier-Cooper Fire Alarm Design Guide, which I hope explains things:
There are two principal methods of smoke detection: the ionisation chamber, and the optical scatter chamber. The detection method chosen will usually depend on the type of fire risk to be protected against. In the ionisation chamber, an electric current flows between two electrodes and is reduced by smoke. Ionisation detectors are particularly sensitive to small particle smoke such as that produced in rapidly burning fires but are relatively insensitive to large particle smoke such as that produced by overheated PVC or smouldering polyurethane foam. In the optical chamber, light is scattered, or in some cases absorbed by smoke. Optical detectors are more sensitive to large particles found in optically dense smoke, but are less sensitive to the small particle smoke. Today, optical smoke detectors are more widely used than ionisation types due to the growing use of flame retardant materials in building construction, decoration and furnishings. Careful consideration must be given to any specific risks that might occur.
I too have been searching for a dual system AC wired smoke alarm. Haven't found one even though I have been searching pretty hard. No one seems to make one.
In any event, you would be well advised to check out the August 2001 issue of Consumer Reports magazine which includes an article with reviews of smoke alarms. They have a useful ratings section in which they break down smoke alarms in separate categories for DC vs AC and ionization vs. photoelectric.
If you really want to have both protection from ionization and photoelectric you will have to get two separate AC units. I have already decided to do that.
The ratings show that within each category the alarms are basically the same in overall performance. Some are rated better for resistance to false alarms though.
I would check out the respective websites of the various manufacturers to see the latest models that are on offer with the most up-to-date model numbers since old models are removed from the market and new models seem to come on to the market quite often.
I have chosen to get the Kidde PE120 photoelectric type smoke alarm and the Kidde 1275K ionization type smoke alarm. Both offer battery backup.
Other modells are available from Firex and BRK/First Alert. I suppose if you stick to a brand name then you can't go wrong. However, my hunch is it is probably best to stay with the same manufacturer if you do get two different models for the sake of compatibility.
The website for Firex is maplechase.com/firex
The website for BRK/First Alert is firstalert.com
The website for Kidde is kiddesafety.com
Wishing you all the best in your hunt.
#17535 - 11/28/0211:11 AMRe: Smokes, Ionization or Photoelectric?
Seems like the smoke detectors has always been a subject of discussion, which style is better. I know here in Massachusetts the fire dept. now want photo electric installed. They have to all be interconnected with one on every level including the basement as well as one in every bedroom. I asked many fire depts why they chose photo over ion, their replys were that ion have nuscence alarms and people were removing them and forgetting they were removed.
#17536 - 11/28/0203:17 PMRe: Smokes, Ionization or Photoelectric?
Thanks for all the usefull information. It's funny, I've installed plenty of smokes but never thought about which one is best untill it came to my own house. I too live in Mass. and was unaware that the local fire departments had a preference as to which type to use. I'll have to check with my local fire department. Thanks again for the information.
#17538 - 11/29/0208:27 AMRe: Smokes, Ionization or Photoelectric?
Mass here also and I am unaware of any requirements for smoke detector type requirements by local FD's. My understanding is the Mass building code requires photo electric if located within 10 feet of a bath or kitchen and ionization for the rest. And also NEVER on a dedicated circuit. Wirenutt feel free to st me straight on this.
#17539 - 11/29/0210:12 AMRe: Smokes, Ionization or Photoelectric?
Elecmanscott; Whenever I wired a new home in MAss. it was suggested by the ahj to have the smoke detectors located and approved by the local F.D. I would bring a set of plans to the F.D.. They would hi-lite location and type on the plans. After ahj inspected the home, the F.D. would come in and test the units with simulated smoke. If approved the F.D. would issue a certificate of approval. I would tell the homeowner to make a copy and send one to their home owners insurance policy.
#17540 - 12/01/0210:59 PMRe: Smokes, Ionization or Photoelectric?
Wirenutt now that you mention it, I recently did an addition to a single family ranch and the building inspector sent the homeowner to the local FD with the plans and they marked the locations they wanted. Although they did not specifiy which type to use they did want the rest of the house hard wired with smokes.
#17541 - 12/02/0211:16 AMRe: Smokes, Ionization or Photoelectric?
What about heat detectors? I thought it would be a good idea to install one, but after I got it, I noticed the label said it was not a "life safety device". Is this a waste of money? What about heat detectors in attics? I understand they make units designed for the high heat of an attic (where smoke detectors don't work well, I hear).