Yes, of course, forehead thermometers can be used outdoors. But, you need to ensure that the area is not directly exposed to the sun. In other words, avoid checking the temperature in extremely heaty environments or near radiant heat sources. Ensure that the forehead's test area is clean, dry and not blocked during measurement. And the most important thing. The temperature at the forehead test area should not increase or decrease by wearing head covers such as bandanas or any sort of excessive clothing. Or, by making use of facial cleansing products such as cosmetic wipes.