This technology has been around for a few years, I'm told, but I just had my first experience with it.

Stopped at the Safeway on North Charles, and I parked on the street with the expectation of running into the supermarket and picking up some plums. (I usually park in the parking lot.)

Once in the store, I realized I needed more than just plums, so I grabbed a shopping cart and, quicker than you can say Pork-Chop-Special, I had a full cart of groceries.

Paid for my stuff.

Pushed the cart out of the store, down the walkway toward Charles Street and my car.

Got about one foot past the end of the store and the wheels of the shopping cart locked. I stopped short. At first I figured the wheels had gone funky, as they sometimes do. It was suddenly quite weird -- I couldn't budge the thing. It was as if the cart were being held to the pavement by a super-magnet. Then I noticed the sign on the inside of the cart:

This cart protected by anti-theft device. Wheels will lock.

As a Safeway employe explained, there's an electric fence in the pavement, marked with a yellow line I had never noticed before, and a sensor in the cart. Try to push the cart over the line and, slamm-o, you're done. No curbside parcel pickup for you!

Here's more info from The Raw Feed and Metroactive