Public hot-spot operators have a weapon in their protest against the growth of commercial Wi-Fi networks: Michael Oh's "war car."

The 1997 Saturn has enough Wi-Fi equipment installed on its bumper and rooftop to create a 150-foot wireless network, said Oh, who helps run a free wireless network covering two Boston city blocks and is one of hundreds of so-called public hot-spot operators who believe Wi-Fi networks and the Internet access they offer should remain free.

The war car's first sortie was nine days ago to a Starbucks cafe, where Wi-Fi access is sold by the minute.

Oh parked the car outside the cafe and fired up the network. Because the vehicle was close enough to the shop, laptop users inside the Starbucks--which charges up to $2.50 for 15 minutes of access--could use his free network. "A couple of people logged on," he said.

Supporters of free Web access were among the first to set up the 300-foot zones of wireless access that Wi-Fi created in the mid 1990s, primarily in large cities like New York.

Companies such as T-Mobile and EarthLink founder Sky Dayton's Boingo Wireless began selling access to their own Wi-Fi networks about two years ago. They charge for monthly, weekly or daily access.

But why pay for it, Oh said, when it's readily available elsewhere for free?

"I'm trying to prove a point by poking a hole in their business model," Oh said. "Maybe it's the store next door to Starbucks providing the free access. The point is there'd be nothing Starbucks could do about it."

Oh has since released a way to assemble the war car from commercially available Wi-Fi equipment. There have been scores of downloads in the nine days since the specs release, he said, though he didn't release a specific number.

A Starbucks representative could not be reached Friday for comment. A representative at Wireless carrier T-Mobile, which supplies Starbucks with the access, declined to comment.

The war car uses a new technology developed by Oh and others at Tech Superpower, a Boston-based consultant specializing in products made by Apple Computer.

The car is fed broadband Internet access that arrives wirelessly from Tech Superpowers' offices, coming via an access point--which creates the wireless zones--sitting on top of the car's roof, Oh said. The car can roam about 1,500 feet from the offices' antenna. Normally, Wi-Fi access points need to be connected to the Internet, whether using a DSL (digital subscriber line) or cable modem; and most are plugged in using wires.