These remotes and openers came around 1993-1997 which was after the Chamberlain DIP switch remotes but before Security+.
Transmits on 390Mhz. FCC ID: HBW0710
The two remotes that I have are model 81LM which are both single-button. Some research suggests that 82LM and 83LM also exist, which have 2 and 3 buttons respectively. The chip used in the remote looks like it is from Texas Instruments with part number 125C79
81lm_1.sub (29.9 KB)
81lm_2.sub (33.7 KB)