Time travelers, as do any tourists, will inevitably get lost now and then (no pun intended). This is intended as a guidebook to help a lost traveler figure out when they are.
Technology changes rapidly, and many things take on different shapes or sizes once they are first invented. This list shows only the initial invention, since a guide to the many kinds of automobiles (for example) would be quite large indeed. Furthermore, the guide uses only objects that would be easily found or well-known after their introduction.
If you find one of the following inventions, you may be assured you are visiting a time at least as late as it first appeared:
Motion picture with sound: 1910
Traffic signal: 1923
Telephone answering machine: 1935
Credit card: 1950
Solar cell: 1954
Artificial satellite: 1957
Synthetic grass: 1965
Automatic teller machine: 1969
Video game: 1972
Reusable spacecraft: 1981
For the benefit of lost time travelers, writeups in this node will be integrated. It would be very helpful to have lists for the 19th century and earlier periods.