A Minnesota entrepreneur hopes a computerized sonar device is the answer for illuminating the rearward blind spots that plague drivers of bulky trucks and recreational vehicles.

The blind-spot scanner, which will which cost $400 to $550 depending on the size of the vehicle using it, signals the driver when a vehicle slips into the black hole by the back wheels of a tractor-trailer or other big truck, out of sight of the rear-view mirror.Marketing the Vehicle Blind Spot Alert is Bill Bartodziej of Edina, an insurance salesman whose work made him aware of a need for such a device.

Many of his clients are truckers who repeatedly have told him of problems stemming from cars that move into their blind spot, one of the most common causes of accidents, said Mr. Bartodziej, 47.

When a truck attempts to turn or change lanes with a car in the blind spot, the results can be fatal for those in the unseen vehicle and expensive for the trucker's insurer.

The blind-spot detector employs sensors are attached to both sides of the vehicle and wired to a small computer on a metal box fitted below the dash. Two small red lights placed on top of the windshield indicate whether another vehicle is in the blind spot - the left light blinks on when a car slips into the left blind spot, and vice-versa.

The device also beeps when the turning signal is turned on and a vehicle is in the blind spot.

It's made me a better driver, Mr. Bartodziej said of the demonstration model he's used in his van for several months. It's made me more alert that there are people around me.

Motor carriers will be the first big target market for the newly formed Freeway Technology Inc., based in Edina and headed by Mr. Bartodziej's wife. He also hopes to sell the device to owners of cumbersome campers and to companies that rent moving trucks.

With the patent application still pending, Mr. Bartodziej made his first sales at the end of March and put field representatives to work in Minnesota, Wisconsin and Illinois. He plans to embark on a national sales effort by August, he said.

The detector was developed by David Ziembicki of Indian Valley Manufacturing of Telfore, Pa. Mr. Bartodziej, who knew Mr. Ziembicki from a business contact, urged him to tackle the blind spot with some technology he was developing in work on an unrelated product.