In Reiki scanning you hold your hands a little above someone's body and move them slowly. At some point most people notice a difference in one spot, for example a tingling, a warmth that wasn't there before, or a slight resistance in the air. Put simply, you're reading the energetic body with your hands without touching the physical body.
In Reiki this kind of perception isn't an add-on for advanced students. It's part of the practice from the start. In this article I'd like to explain what's behind it and how scanning relates to the perception of byōsen.

What happens when you scan 探査
In Japanese this practice goes by the name Byōsen Reikan Hō 病腺靈感法. You can take it apart character by character. 病腺, going by the characters, means scanning for illness in the body, mind or soul, the ability to notice ahead of time where something is out of balance, 靈感 means spiritual sensing or inspiration, and 法 is the method. In other words, it's the method of noticing through spiritual sensing where something isn't right. That's what the characters mean, not a diagnosis.
What the hands feel differs from person to person. Often it's warmth, coolness, tingling, pulsing, density or a kind of emptiness. Some practitioners also perceive colors, images or moods. It matters to me to say clearly that this is an energetic perception and not a medical finding, and that scanning doesn't replace seeing a doctor.
Scanning and byōsen 病腺
Scanning and byōsen belong together. Scanning is the movement of the hands over the energy field, and byōsen is the ability to recognize along the way where something isn't right. What you feel in your hand when a spot gets hot, tingles or throbs is called hibiki, and when you give Reiki, both happen at the same time. I explain more in the article on hibiki and byōsen.
In Shingon Reiki, scanning is a natural part of every session. It shows you where your hands are needed, and that gives you a kind of map of the energetic body that the session follows.
Fixed hand positions and free perception 手
Many Reiki lineages use a fixed sequence of hand positions, from the head over the shoulders and belly down to the legs. That's easy to pass on and makes sure no area gets left out. Strictly speaking, a sequence like that is already a kind of scanning, because from one position to the next you notice where a lot of energy flows and where it doesn't. The perception gets a little finer with every session, and in Shingon Reiki we combine both.
How this perception grows 開発
The good news is that you don't need any special gift for this. Some people notice it right away, others need a few days or weeks of regular practice. Even if you feel nothing at all in one spot, that's a perception too, because often the energy is simply flowing freely there. How to practice scanning and build it into a session is something you experience in the shared practice in the community and at the live events. It's much easier to get a feel for with your own hands than from a text.

You'll find more on the Japanese background in the article on Japanese Reiki techniques. What do your hands feel when you hold them slowly over a person or an animal?
Develop your Byōsen perception
In Shingon Reiki, perception in the hands is part of the practice from the start and grows layer by layer. If you like, take a look at which starting point fits you.
Your path into Shingon Reiki Hibiki and Byōsen