Its controller uses an Arduino Nano to disconnect the system from the internet during times when it's not in use. They're building everything on Mozilla's open smart home gateway software. The system's microphone is a separate USB device that can be easily unplugged. For extra security, the devices don't even use wifi to communicate.
According to its advertising bumph for Dutch Design Week:
"The Candle devices offer the advantages of a smart home system -- such as voice control, handy automation and useful insights -- without the downsides of sending your data to the cloud and feeling watched in your own home. Most smart devices promise us an easier life, but they increasingly disappoint; they eavesdrop, share our data with countless third parties, and offer attractive targets to hackers. Candle is different. Your data never leaves your home, all devices work fine without an internet connection, and everything is open source and transparent."