I’m thinking a la *Star Trek * or The Fly (minus the household pest) and effects social, economic, political, whatever …
It would make some types of crime much easier and also make it harder to establish an alibi if you are falsely accused.
Most obviously there’s the logistical nightmare of border patrol, contraband and yes, Donald, terrorism.
OTOH, travel anywhere would be almost trivial, and I could visit my family and friends hundreds or thousands of miles away.
OTOOH, I’d never use the device, because I’m on the philosophical side of thinking such a device kills you (the original) and makes a copy on the other side who believes they’re you. So… I’ll just let my loved ones come to me while I continue to drive or fly.
Military deployment would be a dream. Though that depends on what side you’re on. So I guess it’d really be a nightmare.
Best of all: Shipping of goods. Order on Amazon (or a pizza) and it materializes in your house in a minute. Yes, please.
Accidental duplication?
Larry Niven wrote about flash mobs, where, say, a million people see something on the news and decide it would be really neat to check it out in person.
In a MINUTE? But I want it NOOOWWWW!
Western societies would quickly get very crowded. It is happening now with Syrian migration to Europe. Central Americans and Mexicans migrating north, etc. Imagine what teleporters would enable. Not just from those countries, but from every third world area of the world. These teleporters would be massively destabilizing.
Pattaya Beach Thailand would also get very crowded.
Nitpick: a transponder is short for transmitter-responder; it’s a radio communication device that responds to or repeats incoming transmission. Like the ones on airliners that announce their identity.
How an instant transporter will change society will depend on how expensive it is, what the range is (limited to terrestrial travel?), and whether it can transport you to any location, or only to dedicated receiving stations.
I think in any case, to begin with, it’ll just be a replacement for business jets. Eventually, as it gets cheap enough for commuting, it will spread suburban sprawl to the whole Earth (you could live on a tropical island or the middle of the rainforest and still commute to your job in the city).
Real estate prices would vary wildly.
Jet lag would be epic. At least now, it takes a good 12 hours to get to the other side of the planet, minimum, and you can sleep through part of that. Try getting up at dawn, hopping into the transporter, and it’s bedtime wherever you are…
Right. Beaming human around the word would be an unanticipated result of using a transponder.
And Mecca?
On the other hand, it might dilute some aspects of tourism, with a lot of distant and hostile places becoming more accessible. Can we reach the Moon?
Do we need a device at either end, or is it like Star Trek?
If the latter, top of my list would be skydiving, wingsuit flying, free climbing. Teleport to any chosen height or location (including mid-air) to begin; rescue from mid-air by teleport if fall or other disaster strikes.
On a similar note, transporters would greatly ease evacuation from a disaster like the Pacific Tsunami or a high rise fire; and would aid first responders getting to the danger zone.
If it had enough range (say, about 36,000 miles), placing satellites in geosynch orbit would be a snap. Plus, we could start clearing up all that debris that’s orbiting and creating a navigational hazard.
Assuming we have transporters, we would also have shielding technology to protect private homes and businesses. Star Trek-style transporters can’t beam through force shields.
Also, transporters could keep logs of who uses them. They would record the DNA patterns of whoever transports.
Of course, we are unwittingly providing examples of things that do not answer the OP’s criterion.
Well, it’s hard to answer. Since we don’t have transporters yet, we won’t encounter any unanticipated problems until they occur. At the present time, it’s unknowable.