A study published in the BMJ found that this method cut systolic BP in hypertensive patients by nearly 14mmHg compared with manual readings.
A GP expert on BP measurement said the device could help reduce the clinical impact of white coat hypertension - anxiety caused by visiting a doctor.
Researchers led by Professor Martin Myers of the University of Toronto allocated 303 patients to BP measurement by automated meters, which take six BP readings at two-minute intervals. A control group of 252 patients received routine manual measurement.
Researchers then compared readings with patients' awake ambulatory BP.
Mean systolic BP in the intervention group was 135.6mmHg using the automated system, compared with 149.5mmHg before enrolment.
In the control group, mean systolic BP also decreased slightly, although this could be explained by increased drug compliance among patients, researchers said.
The researchers concluded: 'Replacement of manual office BP measurement with automated office BP virtually eliminated the difference between the routine manual office BP and the awake ambulatory BP (white coat effect).'
Birmingham GP Professor Richard McManus, professor of primary care cardiovascular research at the University of Birmingham, welcomed the findings.
He said the device could help reduce risks of unnecessary treatment caused by the white coat effect.
'There might also be benefits, in terms of cost effectiveness and of identifying patients with white coat syndrome. This machine may be a way of doing that,' he said.