Stolen iPhones are becoming worthless to thieves.

London has a serious phone theft problem. Around 200 phones get stolen there every day. So it stands out when thefts dropped 18 percent in a single year, and almost 46 percent in the hardest-hit part of the city.

Driving that drop is what happens to a phone after someone swipes it. Apple has spent the last couple of years making stolen iPhones much harder to sell, and British police say it is working.

Apple strengthened a feature called Stolen Device Protection in its latest iPhone update. Before, a thief who knew your passcode, or who grabbed your phone while it was still unlocked, could wipe it, sign your account out, and set it up clean for resale. Now the phone asks for your face or your fingerprint before it will make those changes. Your passcode alone will not be enough. Being able to wipe and resell the iPhone is what gives it value to a thief. Take that away and the phone is worth a fraction of what it was.

The Metropolitan Police in London started handing Apple the identifiers of phones reported stolen. In return, Apple tells them when one of those phones tries to come back online or get reactivated. That gives investigators a picture of where stolen phones end up. Usually switched back on a few streets over, shipped overseas, or stripped for parts. The Met's commissioner says Apple believes it has "cracked" the engineering side of the problem.

Not all progress can be attributed to Apple. The Met has said Samsung and Google are tightening the same screws. The commissioner is pushing the government to require the same from every maker and carrier, not just Apple. The whole industry is drifting toward the same idea. A stolen phone should be a brick.

A lot of security news boils down to "you need to be more careful." This is the rare story where someone else put in the work. You aren't completely off the hook though. Newer iPhones may have it on by default, but plenty of phones do not. Luckily it takes about two minutes to check.

What you can do:

• Turn on Stolen Device Protection. Go to Settings > Face ID & Passcode > Stolen Device Protection and switch it on. You will need Find My, a passcode, Face ID or Touch ID, and two-factor on your Apple Account. Most people already have all four.
• Set it to Always. The default only kicks in away from familiar places like home and work. "Always" is one extra tap and covers you everywhere.
• Make sure Find My is on. It is what lets you lock or erase the phone from another device if it does go missing.
• Trim your lock screen. Keep texts and verification codes from showing on a locked screen, so a thief cannot read a login code without getting in first.
• Buying a used phone? Finish setup with the seller there. That is how you confirm it is not still locked to someone else's account or flagged as stolen.

These numbers are London's, and the police data-sharing piece is a British arrangement, so the picture in the States will likely look different. There is a real downside as well. If a phone gets wrongly flagged as stolen, the same locks that stop thieves can shut out the rightful owner. The way you appeal that is not spelled out well yet. Repair shops and refurbishers may have a harder time doing honest work, too.

Open Settings tonight and make sure Stolen Device Protection is on. A thief who grabs your phone should end up with a paperweight, not a payday.

Sources: The London theft figures and the Apple agreement come from the Metropolitan Police. Spotted via Malwarebytes.