People who don't volunteer for snitching device may end up with higher rates by default.

More auto insurance companies are asking customers to ride around with a little electronic tattletale.

The device is the size of your palm. Plug it into your car and it will tattle to the insurer about how fast you drive, the time of day and the mileage. It will snitch if you peel out from stop signs or brake hard. Some versions measure how hard you turn.

The insurer will use all that to decide how much to charge you.

Easygoing drivers will get lower rates, especially if they don't drive far. Lead foots won't. Neither night workers nor people with long commutes will benefit.

The programs are voluntary, so expect good drivers to sign up for monitoring while bad drivers shun it. Consumer advocates worry that people who don't volunteer may end up with higher rates by default as they are lumped in a pool of bad drivers. Some also criticize the programs for penalizing late-night driving, noting that night workers have no choice.

Allstate's "Drive Wise" program is active in Illinois and will roll out in Missouri during the first half of this year. Progressive is actively pushing its "Snapshot" device on St. Louis TV. The devices communicate via cell towers.

State Farm, by far the largest auto insurer in St. Louis, offers a program in Illinois and will roll it out in Missouri this winter. Customers must have a car with General Motors' Onstar system, Ford's Sync or the competing In-Drive service to participate in the State Farm program.

Insurance companies say it's an effort to price insurance by the riskiness of the driver, and that it encourages good driving.

"It does make you think," says Stephanie Howell, spokeswoman for Allstate. "It rewards you for safe driving habits."

The companies generally don't monitor where you drive, so they can't tell if you're speeding. State Farm, however, will mark you down for driving over 80 miles per hour.

I tried Progressive's Snapshot device for a month. I had no trouble plugging the monitor into the diagnostic port under the dashboard of my Buick. I printed out a picture of the location from Progressive's website.

Driving with Snapshot is like having a nanny hiding in the seat well. It beeped at me when I braked too hard or floored it up the ramp to Highway 40. Each beep, I knew, was a demerit that could mean a higher insurance quote.

Like some other programs, Progressive lets you keep track of your performance on its website, measuring your braking, acceleration and mileage. It grades you as excellent, good or "opportunity," which is a nice way of saying "no discount for you, bub."

It also awards little online merit badges. I got one for "alien abduction," since I left town and didn't drive for a week. When I finished the tryout, the system offered me an initial 12 percent discount from Progressive's normal rate. I'm considering this device.

There was only one minor glitch with Snapshot: I use the Onstar communications and monitoring service. The Progressive device blocked the normal monthly maintenance report I get by email from Onstar.

Progressive's drivers keep the monitor for six months in order for the company to set a long-term rate, and the insurer reserves the option of requiring a second round of monitoring. State Farm requires three months of monitoring.

Cheaper rates are the big lure for drivers. State Farm offers a 5 percent cut just for trying it. Allstate offers 10 percent off.

If nice drivers are rewarded, will a daredevil eventually get punished with a higher rates? "If you don't like the program, you can always get out of it," says State Farm spokesman Jim Camoriano.

Insurance companies are still tweaking their ratings systems, but they say it's clear that hard braking and rapid takeoffs mean more accidents.

"You can see who is defensive and who is aggressive," said Richard Hutchinson, Progressive's general manager for usage-based insurance. "It gives us very powerful data from an insurance standpoint."

More controversial is the decision to rate late-night drivers lower. Hutchinson says midnight to 4 a.m. is statistically the most dangerous time to drive. Rush hour is middling in danger, while other times are safer.

Consumer Watchdog, a California group active in car insurance issues, hates the idea of penalizing night owls. Lots of people have to work nights, and that doesn't make them accident prone, executive director Carmen Balber says.

By contrast, the group likes the idea of rating drivers by miles driven, known as pay-as-you-drive. "The longer you're on the road, the more likely you'll get hit," says Balber.

A 2008 study by the Brookings Institution estimated that driving nationwide would drop by 8 percent if insurance rates were set by mileage, as thrifty people would alter their driving habits. That would cut carbon dioxide emissions by 2 percent and oil consumption by 4 percent.

The same study confirmed that high-mileage drivers crash more than others. That doesn't mean they are worse drivers; in fact, they come out a little better than others when measured by accidents per mile driven.

Balber is troubled by the "Big Brother" aspect of monitoring.

"Do you know everything they're collecting? And what else might they use it for?" she asks.

Progressive says that 25 to 30 percent of customers opt for the monitors, and they earn discounts averaging 10 percent. The insurer acknowledges that good drivers tend to sign up, while bad drivers don't.

That poses another problem for people concerned with privacy, Balber says. Will they be left in the remaining pool with a lot of bad drivers and end up paying higher rates?

"You should not have to give up your privacy to get a good insurance rate," she says.

Some parents use the systems to monitor their teenagers' driving. Camoriano got a surprise when he plugged in his daughter's car.

"I got a worse score than she did," he said.

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