We've tried a couple at the OPSes and found that this is the best one: https://stethoscope.ca/diagnostix-2100-digital-fingertip-pulse-oximeter.html?gclid=CjwKCAiAlvnfBRA1EiwAVOEgfM6R096RuSc4DarySdi0RZ8aJklxK08swEHS8RNV-17DPqBmq4dKxoCJ24QAvD_BwE
They are pretty reliable and don't break as easily as the others.