Two smart switches will do the job. Most smart switches (eg Zooz Zen71) support three-way wiring, so you can replace the switch at the bottom of the stairs with the smart switch, leave the switch at the top of the stairs, and you’ve retained your existing functionality - but now it’s smart.
Then you can install a second switch at the end of the downstairs hall and program it to join the same group as the first switch. They even make battery versions in case you don’t have power near your new box (Zooz Zen34)
Install one smart switch at the end of the hall downstairs, wired for power but not connected to any load. Replace
Two smart switches will do the job. Most smart switches (eg Zooz Zen71) support three-way wiring, so you can replace the switch at the bottom of the stairs with the smart switch, leave the switch at the top of the stairs, and you’ve retained your existing functionality - but now it’s smart.
Then you can install a second switch at the end of the downstairs hall and program it to join the same group as the first switch. They even make battery versions in case you don’t have power near your new box (Zooz Zen34)
Install one smart switch at the end of the hall downstairs, wired for power but not connected to any load. Replace