There's a lot of power in that tiny device and as a result, the device gets warm after about 20 minutes of use".  If your pet is experiencing discomfort due to device temperature, there is a MedcoVet "hack" that can ease the heating of the device.  Place the Luma in a ziploc bag (to prevent moisture from entering) and place in the fridge for 15 minutes before treating.  This will cool the internal components and will result in longer treatments before the device warms up