SCRAM: How does it work?

July 14, 2010

Brit Trogen


Science in seconds blog brit trogen


As someone with a natural curiosity for all things science, and a rather disturbing tendency to occasionally read *cough*gossip blogs*cough*, I’ve been more than a little eager to explore the workings of the mysterious device called the SCRAM bracelet.

I’ll admit, I’d never even heard of it before it turned up on the ankle of everyone’s favorite actress-turned-tabloid-fodder (though, to my surprise, the “Secure Continuous Remote Alcohol Monitoring” device was first released for public use in 2003), but it’s been a source of constant fascination since then. How does it work? And could Lilo really figure out a way to fool it?! She was pretty sneaky in the Parent Trap…

As it turns out, measuring blood alcohol content via perspiration is a technique that’s been around since the 1930’s, beginning when Scandinavian researchers Nyman and Palmlöv discovered that about 0.8% of ingested alcohol crosses the skin in sweat and vapor. Since then, we’ve learned that ethanol excretions in sweat are highly correlated with blood values, making them a pretty good standard to measure alcohol ingestion (more accurate, in fact, than alveoli vapor—the target of the common breathalyzer).

So, what about the alleged loophole of someone spilling a drink on your SCRAM anklet and setting it off by accident? According to the manufacturer’s website, in addition to consuming alcohol, exposing your SCRAM to alcohol-containing beverages can in fact result in a false positive reading. But there’s a catch.

This is a graph of the SCRAM registering a “drinking event”—someone who has ingested and metabolized alcohol that later showed up in a time lagged-response through their sweat. A “spill event” graph would look very different—a sharp spike in the graph, followed by a rapid drop. An offender could claim that a spilled drink had caused a false alarm, but unfortunately for them, graphs don’t lie.

No matter which way you slice it, you can’t scam the SCRAM. 



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