There is no power off button on iHealth PT3 thermometer, one button for iHealth PT3 thermometer for easy using. If no more measuring is required simply let the device sit idle for 8 seconds to power off automatically.
*credit to Sylvain of iHealth Labs EU
https://helpcenter.ihealthlabs.eu/hc/en-gb/articles/360007212837-iHealth-PT3-Cannot-power-off