A heart rate of over 220 BPM sounds alarmingly high. I think the advice around checking the gadget and its accuracy is good. You could, if you wish take your own pulse although it would be very difficult to count at such a high rate. Try counting over six seconds and multiplying by ten. I am also presuming that you did not have any symptoms whilst having ? such a high HR?? If you did then a trip to your GP would be advisable. There are many formulae to calculate whay you max HR might be but ost use the 220 minus your age formula.