Whether to buy an extended warranty or service plan for a new gadget is a question for most shoppers. Now, with more players in the marketplace, where to buy one may be the more important question.

In most cases, protection plans aren t a great deal. Painting it with a broad brush, it s usually a bad idea, says Dan Ackerman, a senior editor with electronics review site CNET. You re going to spend more buying the warranty than you ll get back [in protection].

Still sold on the idea? There are plenty of options. Manufacturers including Dell and Apple offer them, as do retailers such as Best Buy and Wal-Mart. There are also third-party sellers, notably SquareTrade.com.

Earlier this week, Sony expanded its warranty options, announcing offerings for extended service plans on its PlayStation 3 and PlayStation Portable. Plans extend the original manufacturer s warranty another one to two years. PS3 plans cost $45 for one year, $60 for two, while the PSP plans cost $30 and $40. Sony also now offers an accidental damage plan for the PSP ($40 for one year, $50 for two) to cover accidental screen damage as well as normal warranty coverage. Sony did not return calls for comment.

While gadget servicing plans typically don t make sense for consumers, they ve spawned a booming business for companies, especially as consumers buy more (and more complex) devices, says Matt Healey, the research manager at information-technology market research firm IDC. Industry revenue from selling extended warranty services and support packages is expected to reach $3.6 billion by 2012, up from $1.9 billion in 2007, according to an IDC report.

If you look under the hood of the policies, you ll see the same underwriters, says Vipin Jain, the chief executive of Retrevo.com, an online electronics marketplace that offers user manuals and consumer reviews. But there s still a wide variety in terms depending on what the middle-man manufacturer, retailer or other vendor wants to offer.

Consider these seven factors before you sign up for a deal:

Type of protection

Read expert and consumer reviews to see what problems crop up for a particular item, and then look to see which vendors offer plans that fit those circumstances, says Michael Carnell, the founder of Charleston, S.C., information technology firm Palmettobug Digital. Extended warranties cover only problems that result from normal use of the product, while insurance or protection plans handle theft or accidental damage. A service plan covers some combination of the two and may also provide assistance on setting up or using a device. Whatever is covered should be what s likely to go wrong, he says.

Pay special attention to the fine print on coverage. It s very important to look at what s explicitly left out or not explicitly covered, Carnell says. Data stored on the device, for example, usually isn t protected.

Before paying for gadget protection, make sure you aren t already covered for free. Many credit-card issuers automatically extend manufacturer warranties on purchases made with their card, Ackerman says. Costco also provides a complimentary warranty extension on televisions, computers and projectors, covering them for two years from the date of purchase. Some items may even be covered under a homeowner's or renter's insurance policy.

Cost

Retailers use of extended warranties as a profit generator adds to the bill. Buying directly through the manufacturer or an independent third party is typically cheaper, but not always. For example, Best Buy charges $90 for a two-year protection plan on a $700 46-inch Sony Bravia LCD. At SquareTrade.com, $90 gets you three years of protection. The cost through Sony is $55 for two years and $95 for three.

The price gap widens with the likelihood that the item will need repair during the warranty period, Jain says. An extended warranty on a laptop computer, for example, might cost up to 35% of the purchase price in stores; twice what a manufacturer or retailer would charge.

Brand

Don t buy a plan without the confidence that its vendor will still exist for another three to five years until coverage expires. Otherwise, calling [needed repairs] in could be difficult, Carnell says. For no-name brands, the store plan is a better choice. Local electronics shop? Stick with the manufacturer, he says.

Repair expertise

For complex gadgets and unusual problems, it s tough to beat the manufacturer. They did make the device, after all, Healey says. Repair technicians are skilled in that specific item and there are parts aplenty already on hand.

Repair shop proximity

Mailing off a covered gadget for repair isn t always convenient (say, for a work laptop) or easy (a fragile flat-screen). Retailer plans have the edge here, since most offer some in-store repair services. If I have a problem, I can just walk in, Jain says. Some may also provide in-home servicing for an additional fee. Manufacturers may offer service through local authorized repair shops; before you bite on the plan, hunt down the nearest location.

Replacement option

If a device proves particularly problem-prone, at what point -- if ever -- does the policy allow for a replacement or a cash refund? If a protected iPhone breaks, they hand you another one. It s fairly painless, Ackerman says.