Shelly relays (or similar smart relays, like the Sonoff Mini) are great for making your dumb switches smart. A limitation however, is that their "light state" can get "out of sync" with the physical one (eg, rocker in On position after the light's been turned off via automation). It can be disorienting or even worse if you have a multi-gang of smart-relay switches in different light and rocker states.
Momentary switches solve this problem: the physical switch always goes back to the same position after releasing it, so there's no confusion about the rocker.
But momentary switches can also make your smart switch smarter: you can distinguish different type of press events with a momentary switch, like long vs short presses or double (or even triple) presses, using smart firmware like Tasmota or the native Shelly firmware. Coupled with Node-red automation, you can give your ordinary light switch special abilities: short press for regular ON/OFF functions, long-presses to turn on all the lights in the room, or double-presses to activate lights in another room.
The problem with momentary switches is that they are hard to come by in the U.S. and relatively expensive (vs normal $1 ones sold at Home Depot).
However, there is a DIY (and economical) option: make your own!
In a few minutes, you can modify your ordinary single-pole Decora rocker switch into a momentary rocker switch, like this:
So let's make own momentary rocker switch from an ordinary rocker switch! (inspired by this post by Emily++)
DISCLAIMER: IF YOU DO NOT HAVE EXPERIENCE NOR UNDERSTAND ELECTRICAL WIRING IN YOUR WALLS, PLEASE CONSULT A PROFESSIONAL ELECTRICIAN. THIS EXPLAINER IS FOR EDUCATIONAL PURPOSES AND IS NOT INTENDED TO BE PROFESSIONAL ADVICE. TOUCHING LIVE WIRES AND MODIFYING YOUR ELECTRICAL DEVICES CAN KILL YOU (AND LIKELY VOID ANY WARRANTIES - whichever is worse for you)
1 - Use a razor or hobby knife to pry out the rocker from the side. It should come out easily.
2 - Remove the rocker and note in the center of the switch is a "metal tab thingy". Take it out. Note it has a "nipple" on the side facing the "top" of the switch. You'll need to put this back later.
3 - Look inside the middle hole where the metal tab used to be. Note there is a contact back in there, that the tab normally presses against. You may need to use a flashlight or bright light to see it.
4 - Use a small screwdriver or other thin tool to reach in and pull it downward, so that the contact bends downward, roughly midway down.
5 - Put the tab thingy back in the middle. Make sure it sits centered as you found it, so you can put the rocker back on fit atop it; it should snap into place. You may have to redo it a few times to ensure they're all aligned.
6 - Your rocker should now be momentary! Test it out. It should offer slight resistance and a light click-sound on press. If it doesn't feel "right" (eg, feels stuck, hard to press), it probably isn't, so retry the previous steps.
7 - Test the circuit with a multimeter circuit-testing function. Ensure the circuit is only CLOSED ("beeping") when pushing IN, and when released, the circuit is OPEN ("no beep")
8 - Rewire it back in the wall and turn the circuit back on.
9 - You now have a DIY momentary switch you can use with your smart relay! Note the light may only stay on when pressing On; upon release, the light will turn Off. If you have a Shelly relay with this light, set it to Momentary switch in Settings, per this explainer. Your lights will then work like this:
Did this work for you? Let me know in the comments below!