Fit a smart smoke alarm

I wanted to install a smart smoke alarm to my printer. I have had a standard one on the Creator Pro but really wanted to move to a smart alarm which could power off the printer if it triggers.

There are numerous makes of alarm but most seem to be ludicrously expensive. However, I then found some generic 433MHz devices which integrate with the Sonoff WiFi bridge. I already have various Sonoff devices (including one on the power for the printer itself) and am using a bridge, so this seemed like a good choice. They were also about a twentieth of the price of options like Nest.

I created a simple bracket to mount the alarm on top of the Z axis gantry.

This simply uses standard T-nuts to mount the device above the height of the gantry, directly above the extruder. 

As it looked a little "industrial" on its own, I also created a simple push-on cover to neaten up the look.

The smoke alarms I am using are these from AliExpress. They seem to be available from various different sellers on there. 

Setting them up was very simple: open the Ewelink app as normal and go to the Bridge. In there, select the option to add a device. Press the button on the alarm and it will beep and send a signal to the bridge, which adds it to the list. Just give it a meaningful name and it's done. 

If you also then install a Sonoff power switch to the printer, it is possible to created a scene in Ewelink which powers off the printer when the alarm is triggered. Alternatively, (or, better still, additionally) it is possible to use IFTTT to create other actions from the same trigger, such as alerts or other smart control functions. Doing the switching directly within Ewelink/Sonoff has the advantage that it is much faster. My tests show the printer powering off in less that a second in this scenario.

One of the things on my to-do list is to set up the BTT UPS function to protect against power outages. Obviously this is going to conflict with the emergency power off, so it's likely that I'll need to add a second switch into the 24V rail when the UPS is installed, so that both mains and 24V are killed at the same time - bypassing the UPS function. 

I hope that it goes without saying that this doesn't make your printer safe from fire. I see it only as a helpful tool in the arsenal of measures you might take. You follow any steps in here entirely at your own discretion and risk. 

The models for this are available for download from Thingiverse and Cults3D

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