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Losing your car keys in 2016 can be an expensive proposition. With the widespread adoption of keyless ignition and keyless entry, most cars now come with a set of miniature computers you carry around to get inside and drive them. They never have to leave your pocket or your purse.

Predictably, those tiny computers and their software are expensive to replace. It can cost up to $400 to replace a modern key fob because of their wireless transmitters and encrypted chips. That’s before you add in the potential cost of reprogramming the car to recognize its new key.

We spoke with John Paul, an ASE-certified technician who works for AAA of Southern New England, to learn the state of the replacement key industry.

His first advice: “Don’t lose your keys!” Doing so is an increasingly expensive hassle.

Temporary Workarounds When You do Lose Your Keys

If your car is older and you’re at home thinking you may be able to find your keys given a little more time, you may be able to make do with a simpler valet key. It won’t have the remote lock and unlock buttons, so you’ll need to lock and unlock your doors the old-fashioned way, using the keyhole on the outside.

Most modern cars no longer have an exposed keyhole, but they still exist someplace in the door handle. Assuming your keys aren’t locked inside your car, check in your owner’s manual to see how to access it. It’s usually under a small plastic plate that you can easily pry off the door handle. It’s not elegant, but it will let you open your door and lock your car without using the fob.

Some cars even have old-fashioned keyholes for the ignition, hidden under a plate on the dashboard, in the steering column, or underneath the start button where you can use a valet key.

Having an original valet key is valuable, because even the most basic keys today have transponders embedded in them that verify their authenticity before allowing the car to start. You can’t just buy a $4 replacement key at Home Depot, use a kiosk machine to cut it, and expect it to start your car. Keys with such chips embedded start at about $40 online. At least the original valet key that came with your car will already have an authorized chip.

If you think you may have locked your keys inside the car, you could get a cheap replacement made that will get you in the door using the hidden keyhole. Then if you find your keys inside, you’ll only be out a few bucks.

Telematics

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Lots of new cars also include telematics systems that go by names such as OnStar (General Motors), mBrace (Mercedes-Benz), and BlueLink (Hyundai). These subscription services can remotely unlock and start your car, either through an app on your cell phone or by making a call to the automaker. That may also help if you’ve locked your keys inside and need to retrieve them. Unfortunately, even with the car unlocked and running, you won’t be able to drive it, because the steering and transmission will remain locked.

New Transponders

If you’re away from home your problems are likely to be bigger. Without access to the car or a replacement key, you will probably have to call a tow truck.

Most new cars require remote transponders to activate push button ignitions and keyless entry systems. You wouldn’t want just anyone to be able to open the door, push the start button, and drive away in your car.

In these cars, a valet key won’t work; you’re going to need a whole new remote. Dealerships charge at least a few hundred bucks for a new key fob with transponder buttons. We looked online and found prices ranging from about $250 to nearly $700.

Another option is to buy a key directly from an online supplier such as ikeyless.com, remotesandkeys.com, or keyless-remotes.com. For most cars, at least those that are not brand new, these sites can save you hundreds of dollars compared with a dealer price.

Reprogramming the Car

Once you get the new transponder, you’ll have to have the car programmed to recognize the new key. On some cars, there may be a simple sequence to follow that will let you reprogram the key yourself. You’ll have to look online to see if the sequence is published for your car. Bear in mind that while it might save you time and money now, in the long it could be problematic to have a car that will allow any strip-it gang to create a new key by looking online.

More recent models require a dealer or a locksmith with specialized electronic tools to program. If you have one of these cars, you can check with a dealership to have it reprogrammed. Many dealers will program a new key fob for free as a customer courtesy, especially if you’re a loyal customer with a newer car. Otherwise, it’s likely to be much cheaper to call a locksmith.

A Special Note for Mercedes-Benz Owners:

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If you have a Mercedes-Benz, you will have to take it to a dealership to get a new key. Without an extra set, your car will be immobile in the meantime.

Mercedes reportedly incorporates the security software to identify keys into the transmission control module, so if you don’t have an authorized key, you won’t be able to shift out of park. Since Mercedes-Benz won’t allow independent shops, including locksmiths, access to its control software, you’ll have no choice but to get a new key from your Mercedes-Benz dealership and have them reprogram it. None of the replacement key sites we listed offers replacements for Mercedes-Benz vehicles. But, we did find some used keys for older models on eBay. Before buying one, check with your dealer to ask if the service department would be willing to reprogram your car to use one.

How to not lose your keys

Given the hassle and cost of losing your keys, it’s clearly better not to lose them in the first place. That’s why several providers, like Tile, TrackR, Lasso, and Pebblebee, now offer electronic tags that you can put on your keyring to help you find your keys. They connect to your cell phone via Bluetooth, so if you lose your keys, you can look on your phone to see where it last “saw” them. If they’re nearby, the phone can let you know how close you are to them – sort of like playing warmer or colder as a kid. As a bonus, if you lose your phone but have your keys, the tags can trigger the phone to ring to help you find it as well.

Several websites have published comparisons of the various key tags, including Wirecutter and Tomsguide. All have named the Tile as the most effective and the best deal.