BALTIMORE • With the holidays in full swing, Americans are bracing themselves for the seasonal onslaught of a new kind of Grinch trying to steal Christmas: The so-called "porch pirate".

These opportunist criminals have emerged as a threat in the era of online shopping - taking parcels from people's doorsteps before they get anywhere near the Christmas tree.

But residents wary of seeing the season of giving turn into a free-for-all among petty crooks are wielding their own weapons against the thieves: ingenuity, technology and good old-fashioned community spirit.

Ms Rosemarie Dumhart, of Baltimore, spends much of her day in a rocking chair looking out at the street and running out to collect for safekeeping any gift she sees delivered to her neighbours.

"We kind of all look after each other on the block," said Ms Dumhart, a 79-year-old retiree who has witnessed the gentrification of her neighbourhood and a change in the way people shop.

"When I moved here 24 years ago, I had bars on the windows to prevent people from breaking in. There was drug trafficking everywhere," she said.

"It is very peaceful now, with a lot of young and educated people. But they all shop online!"

Beyond protecting her neighbours' purchases, she has turned into something of an amateur sleuth, developing a system for snaring miscreants with her neighbour, Rob.

Every time something is delivered to his house while he is away, she collects it and replaces it with a bogus parcel simply containing a bottle of water with the message, "please recycle and reconsider your life choices".

Around 20 thieves have fallen for the bait this year - only to be filmed by a camera above the door. The videos, posted on YouTube and shared with the police, have led to at least one arrest.

A study last year by insurer Insurance Quotes found that nearly 26 million people reported having something stolen from just outside their door during the holiday period.

In recent weeks police and couriers have advised consumers to have packages delivered to workplaces, in safe lockers or at the home of a neighbour who is guaranteed to be in.

They also suggest that people demand packages be left only when signed for, or rig alarm systems with cameras such as those made by the company Ring - now owned by Amazon.

A firm called BoxLock offers a big yellow padlock equipped with a barcode reader that allows a delivery person to leave a parcel safely inside a metal box.

Mr Brad Ruffkess, its founder, came up with the idea after moving in 2016 with his wife from an apartment to a house, outside which several packages were stolen.

"We were looking for a solution and got surprised to see how little existed. Cameras are just a deterrent. They can't physically protect deliveries," Mr Ruffkess said.

On the lighter but more sophisticated side, former Nasa engineer Mark Rober, angry over seeing a package stolen from outside his home in broad daylight, spent months building a gadget to exact revenge on porch pirates.

His pride and joy is a fake gift parcel box that, when opened, lets off a blast of colourful glitter and rapid-fire spritzes of "fart spray".

Cellphones attached to the booby-trapped box film it all and upload the footage to the cloud.

Mr Rober's YouTube video explaining how he built the device and showing thieves' horrified reaction after opening it has been viewed more than 11 million times.

Police in New Jersey have also used bogus packages fitted with GPS devices to track thieves. And just about everywhere in the US, the authorities are waking up to the phenomenon of porch pirates.

"It's obviously not the crime of the century, but it is a crime having a significant impact on our local communities," said Mr Cody Hiland, a lawyer in Arkansas, as he launched Operation Porch Pirate.

"My goal is to make the decision to steal Christmas presents from the porches of people who pay the bills around here a very painful one," he added.

AGENCE FRANCE-PRESSE