"Passive Entry" is indeed the key phrase. A bit of searching shows a bunch of aftermarket systems available on Amazon (among other sites).
Your comment about the passive entry on the Volt got me thinking about using standard Chevy parts. I can't find anything regarding this feature on a 2014 & 2015 ICE Sparks on the Chevy site. I did find these for the 2016 & 2017 ICE Sparks (see p. 4):
http://www.chevrolet.com/content/dam/Ch ... -spark.pdf
And this for the 2017 (see p. 28-29)
http://www.chevrolet.com/content/dam/Ch ... Manual.pdf
The 2015 Spark EV manual shows a spot in the fuse box for a "Passive Entry / Passive Start" fuse. (see p. 261 - fuse 62)
http://www.chevrolet.com/content/dam/Ch ... manual.pdf
The door handles are different on the ICE 2016 & 2017, so I'd have to rework an existing handle to put in the sensor / wiring. Not sure if one would need the fancier '16-'17 2LT key fob. I'm hoping the Spark EV would accept a '16-'17 ICE locking module (or heaven forbid - just plugging in and connecting the sensor to the existing module) in order to activate the feature.