The app also shows promise in making solid predictions about whether the tremor is real or fake.
Withdrawal is a potentially fatal condition that is easily treated with benzodiazepine drugs, a class of sedatives used to treat alcohol withdrawal, anxiety, seizures, insomnia and more.
But physicians are often reluctant to prescribe them because they're frequently abused and can be dangerous when mixed with other drugs, especially alcohol and opiates.
The most commonly used clinical sign of withdrawal is tremor, especially in the hands and arms.
Judging tremor severity is harder than it sounds, it requires considerable medical expertise, and even experienced doctors' estimates can vary widely.
Chronic alcohol abusers often come to the emergency department claiming to be in withdrawal in an effort to obtain benzodiazepines, and it can be difficult for inexperienced clinicians to determine if the patient is actually in withdrawal or "faking" a withdrawal tremor.
Front-line health-care workers had no objective way to tell the sufferers from the fakers, until now.
Researchers at the University of Toronto developed the world's first app to measure tremor strength, providing objective guidance to direct treatment decisions.
A researchers team at Toronto's Schwartz/Reisman Emergency Medicine Institute at Mount Sinai Hospital, St Michael's Hospital and Women's College Hospital tested the app on 49 patients experiencing tremors in the emergency room, and 12 nurses trying to mimic the symptom.
Their study shows that three-quarters of patients with genuine symptoms had tremors with an average peak frequency higher than seven cycles per second.
Only 17 per cent of nurses trying to "fake" a withdrawal tremor were able to produce a tremor with the same characteristics, suggesting that this may be reasonable cut-off for discriminating real from fake.
The app uses data from an iPod's built-in accelerometer to measure the frequency of tremor for both hands for 20 seconds.
In the emergency room, clinicians filmed their patients' hand tremor while using the app and showed the footage to doctors afterward.