In which case no not reliable. As it happens there has just been a discussion about these on one of the drs forums - conclusion being that they are a waste of money. The body surface temperature varies hugely with environmental conditions. Being outside either in the cold or the sun will skew the results. What you need to measure is the body core temperature. If you want to avoid the traditional sort then look at the ear thermometers.
It's for people
For people or materials like water or metal? There is a difference and one posted here a few weeks ago that was used for people. Search for it