As many as 25,000 runners are expected to hit the streets of Seattle this Saturday in the first ever Rock n Roll Seattle marathon -- a festive road race where local bands play music at every milepost. But there's also a unique technological twist -- and runners will find it on their shoes.

Seattle-based Impinj -- along with partner ChronoTrack Systems -- are providing each participant with a radio frequency identification tag that will track start, split and finish times. The companies claim that their weather-resistant tag -- a plastic device known as a D tag that includes a miniature RFID antenna and chip -- is more reliable than other race tracking technologies.

RFID has been used in marathons in the past. But because Impinj uses ultra high frequency RFID tags, Casey Hagen said their system allows race organizers to collect more accurate data at a cheaper price.

"There's a lot more robust data communication," said Hagen, field applications manager at Impinj. "The technology today can not only just read everyone but it can read everyone multiple times and with many data points for the runners running over the line."

That means the system can collect times -- not only at the start and finish -- but also midway through the race and at secret "cheater points" in order to prevent the infamous Rosie Ruiz problem of someone cutting into the race at the last minute. 

The Impinj tags also are disposable, which allows race organizers to automatically match bib numbers to the shoe tags rather than having to input data from older tags.  

This weekend's marathon also marks the first time that Impinj's RFID technology has been on display at a road race in its hometown. 

Running races are actually turning into a sizable business for Impinj, a 9-year-old company which only entered the market last September in conjunction with ChronoTrack.

Evansville, Indiana-based ChronoTrack has now distributed more than two million shoe tags at about 600 races, said Matt Shine, director of marketing.

Impinj spokesman Jim Donaldson declined to say how much money those races have brought in, though he did describe ChronoTrack as a "significant customer."

But why shoe tags? Why not just incorporate the salt grain-sized RFID chip and accompanying antenna into the bib itself?

"That's a good question," said Shine. "That's the holy grail and what everyone is going to in the running industry."

Up until now, companies have stuck with shoe tags because it provides more accurate times by picking up the signal from the thresh-hold antennas on the ground. Putting the tags into the bib is "a more complicated problem," said Hagen.  

But he's confident that the industry will get there.

For now, it is shoe tags.

Saturday's race -- with about 25,000 runners -- will not be the biggest for the companies. They tracked and timed 40,000 runners at the Cooper River Bridge Race in Charleston, South Carolina.

They have had inaccurate counts in the past with older technology, in part because the plastic shoe tag fell off during the race or it didn't get picked up by the antenna. But Hagen says with the new-and-improved UHF technology: "If the tag gets in front of the antenna, we have very reliable reads." (Editor's note: The above statement has been clarified since first being published).

So, now you know who to blame if you don't like your time this Saturday.