If you want to switch your light with Shelly 1, Shelly 1 PM, Shelly 2 or Shelly 2.5 and you do not have a N-conductor at the light switch, you can still use the Shelly.
In this case, the Shelly can be installed directly on the lamp (or of course any other consumer).
The "old" switch serves in this application, on the one hand, the shutdown and the reset of the Shelly.
On the other hand, it can also be used as a light switch simultaneously with the app (in on mode) by appropriate parameterization (see picture).
If you have the Shelly "switched on" so the light can be switched on the app or by home automation (for example Homematic). All other app functions are available.
Here is the schematic that SparkyMaster created: