Assuming the OP is an electronic device (not electrical), it means that it can operate right now.
We are talking about devices that intentionally make use of the properties of interacting electrons in order to produce mechanical power. This would generally refer to actions that occur at sub-microscopic levels, where the effects can be measured but the underlying actions cannot (without tons of test equipment).
If this is a reasonable basis, we could look at Edison’s 1880’s light bulbs. He was annoyed by the soot buildup on the bulbs’ insides. So he thought that current wasn’t just flowing through the filament but also within the vacuum of the bulb. To test if the bulb would be energized by current, he added an electrode to it.
It did, but only when the current flowed in one direction (he was using “direct”) current). Tom likely said, “Aha!” “But what’s the heck do I do now?” He had invent the first diode, unknowingly. He was too busy to sue the people who infringed on his patents so this extra electrode was dropped.
The effect he observed was eventually noticed by John Fleming, an Englishman and electrical engineer who witnessed the “spooky” action at Philadelphia Exhibition of 1884 and tried to perfect it back in London. It was a novelty, though he did it. He did give the bulb a name, the “thermionic vale”. Cool. Maybe warm.
Fleming was hired by Guglielmo Maroni to be a consultant. His valve helped to detect radio signals and developed radio telegraphy, which is a viable commercial method of sending dit-da–dit messages. The Royal Navy and other modern naval navies soon realized the potential of this type of communication. In the meantime, a working model of this valve was made in 1904 and went into production. This was the product that was being made by 1910:
(Credit Vacuum Tube History
)
The New England Wireless and Steam Museum in East Greenwich (Rhode Island) is a prime example of wireless telegraphy. The famed Massie System Wireless Station (PJ) can be found here. The structure is intact and all the equipment is in good working order. If the original tubes found in the equipment are genuine, then they could be considered among the oldest functioning electronic devices in existence. If they are not, I would guess that the oldest working electronic devices are either in a museum of technology or in an attic trunk with radio equipment belonging to a great-great someone. If the tubes aren’t physically damaged, it is possible for them to work if they are fired up today.
We hope that this helps.