According to the NFPA, smoke detectors are good for about 10 years before needing replaced.
Ionization detectors are the least expensive, and are designed to alarm for fast burning fires (ex: Kitchen stove fire, burning waste basket, etc). Because of their technology, these are the most prone to false alarms from dust, steam, smoking pizza, etc. In tests. they were up to 30 minutes slower on detecting smoldering fires (ex, short circuit in a wall socket, cigarette in a couch cushion). They contain a radioactive element, so are not to be disposed of in the trash.
Photo -electric are designed to detect smoldering fires. In tests, they were up to 30 seconds slower in detecting a fast burning fire. They are less prone to false alarms. Can be thrown in the trash after removing any batteries.
As single use, the above are required to be certified by an outside lab. Multi-use units are only required to have the manufacturer have a testing/certification program.
CO (Carbon monoxide) detectors are good for about 7 years before replacement. If you have a combo unit, it needs replacement at the 7 year mark.
The units with the sealed 10 year batteries (most expensive) do not always make it to the ten year mark. Numerous people have had them go dead in 6-8 years and combo CO units as short as 5 (they are only rated for 7 years).
The theory around the inter-linked alarms is that, with one required in every bedroom, they will alert anyone sleeping or behind closed doors to a situation anywhere in the house. If an inter-linked system goes off, the alarm initiating it is the only one that hitting the reset, (opening the battery compartment if that is the fault) will silence them, so if that is a problem, that should key you in on the alarm/location you need to check. If in doubt as to the cause, call 911 and get everyone out of the house.
Our volunteer fire dept gets several calls a month on average for alarms. Most are "false" alarms, however some of those are in fact accurate alarms caused by someone burning food on the stove. Of the truly false alarms, many are solved by replacing the batteries. One of these was an interlinked system, and the alarm at fault was on a cathedral ceiling, thus hard for the home-owner to access for routine battery replacement. If you have an alarm that you can't get to (a stairwell ceiling is another problem location), I recommend you re-locate it. A few were because the alarm was "chirping" for low battery, and the occupant didn't know what that signified. In one case, we discovered that the hardwired, interlinked alarms were a few years past the 10 year mark. The owner was new, having just moved in a week before, and so didn't have any idea how old the alarms were. Although we only found one bad detector, we recommended she replace all of them.
If your alarm has AA or AAA batteries, I recommend you replace them every 6 months. If nine-volt back-up, once a year.
As for my choice when I replaced mine last year (yeah, I was overdue a few years), I put photo-electric in the bedrooms, and a combo ionization/CO alarm in the hallway outside the bedrooms. Mine are interlinked hardwired with battery back-up. In newer homes like mine, the bedrooms should be protected from an electrical short with arc-fault circuit breakers, but I will leave it to the electricians to discuss the reliability of arc-fault breakers.
Hope this helps, from just another anonymous guy on the internet.