Security pens don't use electromagnetic waves. They use ink with special properties to create an invisible mark that can be detected by a UV light.

Here's how it works:

* The Ink: The ink in a security pen contains a fluorescent dye that absorbs UV light and emits visible light in response. This means the ink is invisible under normal light but glows brightly under a UV lamp.

* The Marking: When you write with a security pen, the ink leaves an invisible mark on the document.

* Detection: To check for the security mark, you use a UV lamp. The fluorescent ink will glow, revealing the mark that was previously invisible.

Therefore, security pens rely on the properties of the ink and UV light, not on electromagnetic waves.