Real spies may tell you that their lives are nothing like what you’d see in a Hollywood movie, but don’t be fooled: They’ve still got some pretty cool gadgets.

And aside from the relatively recent tools that monitor electronic correspondence, most of those gizmos have been around for a pretty long time. Spies claim that theirs is the second-oldest profession, and basic espionage needs haven’t changed: looking and listening, getting the information they need, and smuggling it back home.

What has changed is the way those spy gadgets work. As technology advances and enemies get smarter, spies have had to constantly re-invent the tools of their trade.

Click here to see how ancient spy tools stack up next to modern devices.

Long before spy planes and satellites embarked upon aerial reconnaissance missions, ancient Chinese military strategist Sun Tzu (whose classic Art of War contains more than 100 references to spies and intelligence-gathering) described how secret agents could be trained to analyze enemy movements. “Dust spurting up in high straight columns indicates the approach of chariots. When it hangs low and widespread, infantry is approaching,” he wrote. “When birds gather above the camp sites, they are empty.”

And long before scientists knew how to reduce photographic images to the size of a printed period, American Revolutionary troops were relaying messages to one another using an invisible ink called Jay’s Sympathetic Stain.

“Modern spy tools are faster, smaller, more accurate and more easily concealed,” says Peter Earnest, a retired senior CIA official and the executive director of the International Spy Museum. "But they’re the same basic idea as the old ones."

By Leah Hoffmann