The American Heart Association recommends an automatic, cuff-style, bicep (upper-arm) monitor and is the single biggest habit to form to reduce your risk of stroke, heart attack and other cardiovascular events. Heart Habit should be used with an FDA approved, upper arm cuff blood pressure monitor.
Wrist and finger monitors are not recommended because they yield less reliable readings and often not FDA approved. And iPhone apps that claim they can measure using the camera and flash have been proven to be extremely inaccurate and dangerous for you.
Make sure the monitor has been tested, validated and approved by the Association for the Advancement of Medical Instrumentation, the British Hypertension Society and the International Protocol for the Validation of Automated BP Measuring Devices. Also, make sure it meets FDA guidelines.
Make sure the cuff fits. Children and adults with smaller or larger than average-sized arms may need special-sized cuffs. They are available in some pharmacies, from medical supply companies and by direct order from companies that sell BP cuffs. Measure around your upper arm and choose a monitor that comes with the correct size cuff.