A blood pressure monitor is one of the most useful things you can own if you are managing hypertension — but only if you can trust the number. The market is full of cheap devices that produce a figure with no validation behind it, and a figure you cannot trust is worse than no figure at all.
The rule we keep coming back to is simple: buy an upper-arm monitor that appears on the British and Irish Hypertension Society’s validated-devices list. That list is the closest thing to an independent referee. A model that has passed it has been tested against a proper reference standard; a model that merely claims accuracy on the box has told you nothing you can rely on.
Upper-arm cuffs beat wrist devices for home use because wrist position introduces error most people cannot control. Get the cuff size right for your arm — too small reads high, too large reads low — and sit quietly for five minutes before measuring, feet flat, arm supported at heart height. Take two or three readings a minute apart and record the average.
For the readings to be clinically useful, take them at consistent times and bring the log to your GP rather than a single dramatic number. A week of morning-and-evening readings is far more informative than one nervous measurement in the surgery. That is the whole point of self-monitoring: better data, better conversation, better decisions. For the wider context on choosing diagnostic kit, see our full home diagnostics buyer's guide.