I am building a new home and am required to hardwire smoke alarms. I see there are no hardwired wifi compatible smoke alarms (which is nuts) so with that said what would you do?
I am no dummy when it comes to technology but certainly not a coder or advanced user. I am less worried about final integration but am rouging in right now and need to at least act now for what I will need.
Thanks
Scott NB
There is a tread about how to connect hard wired smoke alarms: Connected Smoke Alarms
Sounds like a Kickstarter opportunity! 
Many of us are optimistic for the Fibaro Binary Sensor module. This page even references smoke alarms as a use case.
The question is whether or not you are “allowed to” modify a standard wired smoke alarm to add this or similar module.
You are allowed to do a lot after the fact if you are the homeowner including installing modules. Pizzinini all the threads I found were about converting an existing system to add connectivity. I was wondering how people would do it who could start in a new construction.
I would run all the smoke alarm interconnect wires from the smoke detectors to a panel somewhere for now with AC plug close by so you can do some mod later. Maybe in your electrical room or closet.
If hardwired with wireless interconnect will work nest protects are awesome. Id like to know if anyone has used the Firefighter Smoke Alarm Detector with a Nest Protect. http://www.encorecontrols.com/products.php
The encore controls “firefighter” is a really interesting device. I had thought about something similar before. It’s an acoustic alarm, kind of like a glass break detector, but it has to be really close to the alarm it’s monitoring. Within 6 inches. It’s looking for a specific acoustic signature, in this case the fire alarm, and then sending a wireless signal to a two gig panel or a Honeywell panel. I’m not sure of the exact network protocol being used. It might be a proprietary zig bee. And there’s a lot of additional security stuff built into it. If I had to guess, I would guess that it is not compatible with smartthings, but you could try it and see.
I also just wanted to call out the other detail in your post for those who are not familiar with the individual devices.
NEST PROTECT
Nest protect is not currently compatible with smart things, although who knows what will be added in the future. However it is a networkable smoke detector which is available in either hardwired or battery operated models. From this you can get a notification message sent. So it’s one possibility to consider.
FIRST ALERT ONELINK
The other is the first alert one link, which is also available in either battery operated or hardwired models. In this case most the hardwired models are only intended to communicate with each other. So when one alarm goes off all the alarms in the house go off. However there is a set up option where you use mostly hardwired models, plus one battery operated model, and that gives you some additional Wi-Fi notification options.
Both the hardwired nest protect and the hardwired one link should meet code in jurisdictions that require hardwired detectors. Then if you want to add either The firefighter or the battery operated nest protect it should be fine in terms of a city inspector.
ALARM PANEL ADD ONS
Similarly, if you hardwire to an alarm panel, in many cases you can add a Z wave communication module to the alarm panel rather then to each individual detector.
SECURITY FEATURES MAY BLOCK A ST CONNECTION
Again, it’s unlikely that any of these options will work easily with smartthings at this time. Many security devices, including smoke detectors, use some kind of proprietary method to prevent outside systems from interfering with their operation.
DON’T TRY TO MIX AND MATCH IF YOU WANT A WHOLE HOUSE ALERT
I did also want to mention that most interconnected smoke detectors do not “play nice” with smoke detectors from other manufacturers. It’s just a fact. You will see this warning in the manufacture documentation. Please heed this. If you try to set up a whole house communication network, hard wired or wireless, where one smoke alarm is supposed to trigger another, it really is best if they are identified by the manufacturer as being inter-operable. Otherwise you may get both False Alarms, and fail to trigger events.
I believe this is in part what the “firefighter” device is intended to overcome. As long as the alarm is UL listed as a siren, the sound pattern should be detected by the firefighter device. But I haven’t seen any reviews, I don’t know how well it actually works in practice. But definitely an interesting idea! 
I’m in the same exact boat. Just got dumb units installed and am heading towards the relay option.
I installed the relay a few months ago and it works great. The modification is easy and I can’t see how it would be against code the way the wiring is.
I do really wish someone would build a “proper” device type and also a dedicated piece of hardware for it so people might feel a little more comfortable with the process.
I I think it may come down to whether local code requires a “dedicated” line to the smoke detectors or not. This is sometimes required in some commercial installations, or things like warehouses, I just don’t have any idea whether it ever is in residential or not. If it is, having something else on the line gets trickier.
Did you use the mimo lite and the device type in that post or did you find anything better?
Does it trigger ST when you push the test button on the detectors?