The 1993 federal rule
Every residential garage door opener made for sale in the US since January 1, 1993 has to meet a federal safety standard, 16 CFR Part 1211. It must reverse when the closing door meets an obstruction, and it needs a second safety system on top of that: a pair of photo eyes near the floor at the bottom of the tracks, an edge sensor on the door, or a wall button you have to hold down the whole time the door closes.
If your opener has none of those, it was made before the rule or its safety devices have been taken off. Either way it does not protect anyone in the doorway. Any opener sold new has to meet the standard, including the three in the table above.
Source: 16 CFR Part 1211, the federal safety standard for residential garage door openers (eCFR)