Mastering a power outage in the smart home
Another Sensor
On Amazon, I found another Z-Wave sensor by seven7express (Figure 10) that reports power outages very efficiently. It is implemented as a door sensor and reports closed
if the power is on and open
if not. It is connected to a power outlet via a charger/adapter, whereas the sensor itself has an internal battery that allows it to send signals to the hub via Z-Wave if the wall socket stops supplying power.

The device worked right off the bat. The Groovy script in Listing 2 implements the logic for controlling it. In the preferences
section, the hub looks for sensors with the capability.contactSensor
property and offers the user the newly installed power sensor, among other things, to select from when you launch the app. Line 26 obtains a subscription to the contact
event, which the hub triggers each time the sensor transitions from open
to closed
and vice versa. The script thus notices power outages with only one- or two-second delays and logs them in lines 31 and 33.
Listing 2
power-sensor.groovy
Hello User!
Once the SmartApp determines that the power has gone, it uses the Prowl Web API, as described in a previous article [7], to notify the user who has installed the Prowl app on their cell phone. Listing 3 plants the API key required by Prowl, which registered users can pick up from the website [8] after purchasing the app for $3.
Listing 3
prowl.groovy
The prowl()
function expects a message (Power outage!
or Power back!
) passed in, sets the event field with it, and adds the name of the sending app and a short explanation so the receiver knows where the message came from. In the try
block, httpGet
then issues the web request and checks whether the outcome is good or bad, and log.debug
logs the message for later error analysis. Prowl is a simple and efficient service that works both on iOS and Android (Figure 11).
Web Access
If you enable the slightly hidden OAuth section when setting up the SmartApp on the SmartThings website, you will receive an OAuth token after an OAuth token dance (e.g., via the CPAN OAuth::Cmdline module; Figure 12); you can then access the running SmartApp from the Internet via a web API. The mappings
section of the SmartApp code in Listing 4 defines the entry points of the web API and the actions assigned to them. The checkPower()
function defined in lines 9-13 then reads the current state of the sensor on demand and returns the result as a map, which the web API then returns to the web client in JSON format.
Listing 4
webapi.groovy
Figure 13 shows the query using a curl
client at the command line. First, it asks for the location of the endpoints
stating the API token (i.e., the complete URL under which a registered user can find their SmartApps). Armed with this URL, the client can access the entry points defined in the code (in this example, /power
) and receive JSON-formatted output in return (e.g., the value in the power
field is ok
or not ok
).
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