A fingertip pulse oximeter measures blood oxygen and pulse rate in about ten seconds. It is small, inexpensive and useful when someone at home is older, has a breathing condition, or is being monitored at home on a doctor's advice. Choose a model with an OLED screen readable outdoors and a pulse waveform so you can see whether the signal is stable. Children need a paediatric clip; adult finger clips usually do not fit. Readings can be off with cold hands, nail polish or movement.