You smoked and you're stoned.

But how high are you? Now there's an app for that.

It's called Canary and the $4.99 app launched last week on Apple (AAPL)'s App store.

"This is a first-of-its-kind app to quickly measure how impaired you are from the effects of marijuana," said Marc Silverman, founder of Belles Farm in Boulder, Colorado, the startup behind the app.

The app, he said, isn't meant to replace the THC blood test used by law enforcement to detect marijuana presence.

"It's specifically for recreational or medicinal marijuana users who want to be responsible and not hurt themselves or others as a consequence," he said.

"Maybe you want to take the test before you get into a car, or operate heavy machinery," he said.

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Here's how it works:

The app is based on four quick tests to be completed under three minutes. They measure memory, balance, reaction time and time perception.

"Take the tests for the first time when you're feeling normal" -- not intoxicated in any way -- to establish a baseline, said Silverman.

The app stores that info and then compares subsequent test results to that standard.

"In later tests it will look for anomalies or aberrations to your baseline result," said Silverman. That deviation will indicate how impaired you are.

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The memory test involves a random display of six digits moving around on the screen before disappearing. You have to repeat the same number sequence from memory.

"The balance test mimics the standard field sobriety test used by cops. It measures your postural stand and balance," said Silverman. The app asks you to stand steady on one leg, holding the iPhone close to your body. A tone or vibration signals the start and end of the test.

The reaction time test has a series of buttons of different shapes pop up on the screen and then disappear. As those same buttons reappear on the screen along with new ones, the user must pick only those buttons that were in the original set.

The last test requires users to count out loud for what they think is 20 seconds. The app then determines how close the user was to an actual 20 seconds.

At the end, the app analyzes your total performance against your baseline score.

It then shows a red light (you're impaired), yellow light (possibly impaired), or green light (normal).

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Silverman, an engineer, spent two years developing and testing the app with psychologists and physiologists.

He also taught himself iOS programming and wrote the code for the Canary app himself.

Since it launched, he said the app for iPhones and iPads has been downloaded more than 10,000 times. He plans to have an Android app ready later in the year.