SmartHeart Premium Talking Wrist Blood Pressure Monitor is intended for use in measuring blood pressure and heartbeat rate with wrist circumference ranging from 5.3” to 8.5” inches (about 13.5 – 21.5 cm). Automatic digital blood pressure monitors use the oscillometric method to electronically measure your blood pressure. The monitor detects your blood’s movement through the artery in your arm and converts the movements into a digital reading.