Look for an HRM with digital rather than analog transmission between the sensor strap and the display unit. Digital transmission eliminates false readings due to stray electrical signals. Also look for one that allows you to change the battery rather than sending it to a factory repair station. Do you normally wear corrective lenses, but ride without them? Look for a display large enough to see well in your riding conditions. Look for a unit that is easily removed from the bike when you park and leave it. Some of them come with alarm features to notify you when you have exceded a range you set so you can get back into that range.