Depends what you need with 'smart'

An i4 would detect inputs allowing other actions, but isnt a switching relay

lctham:

just piggybacking off this post, just wondering which Shelley modules do I need to make 4 gang light switches 'smart'? I don't require dimming. Also I have multiple switches controlling the same set of lights, does this complicate things further or just need to put a module into each switch (I will be getting an electrician to do all the installation). Thanks in advance

Look at a 2PM for 2 relays:
https://www.shelly.com/en/products/shop/shelly-plus-2-pm

Stay away from the older Shelly 2.5

So for a 4 gang switch, youd need 2 x 2PM or 4 x Shelly 1

There are some newer gen 3 devices about to be released too

SpookyAwol:

Look at a 2PM for 2 relays:
https://www.shelly.com/en/products/shop/shelly-plus-2-pm

Stay away from the older Shelly 2.5

So for a 4 gang switch, youd need 2 x 2PM or 4 x Shelly 1

 

There are some newer gen 3 devices about to be released too

 

BadCo: 

What's wrong with the Shelly 2.5? The single one I have has been fine.

Likewise till now, but they appear to have a bad rep and have also been discontinued.
Mine are starting to fail and will be replaced

SpookyAwol:

BadCo: 

What's wrong with the Shelly 2.5? The single one I have has been fine.

Likewise till now, but they appear to have a bad rep and have also been discontinued.
Mine are starting to fail and will be replaced

BadCo:

SpookyAwol:

Look at a 2PM for 2 relays:
https://www.shelly.com/en/products/shop/shelly-plus-2-pm

Stay away from the older Shelly 2.5

So for a 4 gang switch, youd need 2 x 2PM or 4 x Shelly 1

 

There are some newer gen 3 devices about to be released too

 

What's wrong with the Shelly 2.5? The single one I have has been fine.

I doubt it would be reasonable to try 4 - the wiring would be a nightmare. 
Are the current switches linked to another switch elsewhere? - ie a shelly could be added to a different switch

I've got a heap of dimmer 2s around the place and have only had one fail (last week) in 4 years. Was a trivial replacement. 

A couple of caveats with the dimmer 2s though. They either work perfectly with you lights or you may have an intermittent tiny flicker - its barely noticeable but has been a big issue for Shelly. They went though multiple firmware updates to try and fix the issue, but never really nailed it. 

There is likely to be a new Dimmer wall module in the next few months and Shelly have indicated that resolving the flicker issue is a focus. I'm planning to try and swap out some of the dimmer 2s where the flicker is most annoyingly obvious as long as Shelly get SDOCs in NZ for the new modules. 

I've also got a couple of 2.5s and some 1s. They've been rock solid. 

lctham:
Thanks, realistically can you fit 4 Shelley 1s in behind a switch?

What are you going to use to trigger the dimmers. I've been looking at momentary switches.

lctham: 

Thanks, realistically can you fit 4 Shelley 1s in behind a switch?

Another (although expensive option) is the PDL wiser range

Alternatively a 4 gang smart switch (tuya) such  as https://www.brilliantlighting.com.au/product/smart-wifi-glass-wall-switch-53dbcf could be used