Demons can smell like sulfur, roses, cologne...anything! They can also appear as: an angel of light, a dead person or child, a spirit guide, a healing spirit (reiki), an alien, a fairy, a dwarf, a spirit animal etc! We can't safely discern them! The safest thing to do, is let Jesus and his angels protect us.
The recommendation is therefore that the stimulation should be applied with a 2500Hz carrier medium frequency sinusoidal alternating current, burst at 50 Hz (10ms ON: 10ms OFF) at a maximum tolerable level.
Definition: A harmonic frequency is a multiple of a fundamental frequency. A fundamental frequency of 500Hz has a first harmonic frequency of 1000Hz, double the fundamental frequency. Its second harmonic is 1500Hz, the third harmonic is 2000Hz and so on.