Drop off a wax cylinder gramophone in 1760 or so, with Ben Franklin or Thomas Jefferson. Plus 30 or so cylinders, & a couple of dozen blanks.
Simple tech, that could easily be replicated in the era.
Well, no.
It needs one telegraph. If someone understands the concept they can as easily build a full size model from one as from two.
It needs a conductor, nothing more. The current can be conducted just as easily along metal plates, or even salt water or a graphite line.
A code is of no significance whatsoever. One if by land two if by sea is as complex as you need for a working telegraph to be of invaluable service.
The classical Greeks had already invented printing, but they rarely used it. So I suspect that the printing press would be lost as rapidly as it was lost in China. It’s an invention whose time must come, and its time is when there is a sizable literate population to both read and write, and a shortage of scribes.
Send a functional hang glider to Da Vinci.
Read the ensuing Dan Brown book laughing all the way.
The fact that I can send something back in time indicates that I have some sort of time machine. I’d send one of those to myself 20 or 30 years ago.
I would appear a (1) lever operated thermonuclear device on the floor of the roman senate(2) to the year 10 BC(3), with a note attached
**
**
freak them out: check
change History:check
No instructions. Use must be somewhat self-evident; so saddles, yes but telegraph, no.
It’s nothing at all impressive to us these days, but I’ve often wondered what a Medieval peasant would make of my contact lenses. I mean, there’s this piece of glass(ish) that I’m putting on my eyeball? And it lets me see better? How f’ed up is that?!
(Of course, I’d have to go back in time with them for full effect.)
I’m skeptical about the whole meme of people standing around with astonished expressions, worshipping the god who brought this device to them etc etc
People aren’t like that. We push and prod things and it’s not long before we can see the limitations of a device we’re presented with. Not long before we can see it is not magic but just a machine with fixed functions.
Being introduced to a technology far beyond what you thought was possible is an experiment that happens thousands of times daily. People don’t freak out.
You must be new here.
to which I’ll add:
A full on, high quality, mountainbike. Mechanics, tolerances, odd materials, and it works without electricity or cellphone towers, or whatnot. It’s behavior can also be determined by observation. Sure, at the right time, a guy may be able to terermine those lines are -wires- on a cellphone motherboard, but what happens in those little black square things?
This is what I was going to suggest, although I was thinking a bit farther back to Antiquity – keeping in mind gramophones played flat disks, but the Edison phonograph and Bell graphophone played wax cylinders (phonograph and gramophone aren’t synonyms).
Howard Goodall’s book Big Bangs, which is about major innovations in music history (musical notation, opera, the piano, etc) posits that nothing ever captured the public’s imagination and excitment the way the debut of the phonograph did in 1877.
Without clicking on it, I know where that link leads to 
Translate the Latin?
Duct Tape. 200 BC
We’d be on the moon by 100 AD
send an iPhone 4G back to Gene Roddenberry, just before they air Star Trek: TOS
While technically possible, I don’t think the lever operated thermonuclear device has been invented yet (for good reasons).
OK, but whatever you use, it’s got to be technologically feasible, in the era you’re sending it back to, to put together a conducting line of one of these materials that extends a greater distance than can be easily serviced by Phidippides and several of his friends stationed at intervals along the way.
The reason we use wire is that it minimizes the mass required to transmit a signal by this means. Sure, you can use metal plates, but who’s going to string together 100 miles’ worth of metal plates, even if there’s no better alternative?
Which link?
What the hoo-ha did Medieval peasants know of clear glass? :dubious:
This one.
I’d send a Gibson Les Paul, a Marshall Stack, and a portable generator back to Beethoven.
What?
;)
ETA: by the way - cool thread. The more serious answers are fun and thought-provoking. What makes the most sense - enabling warfare because that tech is always in demand, or finding the right inflection point to insert a tech which could both gain traction and change the flow of history? The arguments against printing press are intriguing - as are the ideas for the horse collar and saddle and stirrups…