Various "worrywarts" have been concerned for long time about too-smart-for-their-own-good phones being used to spy on naive users using microphones and/or cameras, with GPS location thrown in for free. If you have a smart phone, it could be doing it right now. Don't bother switching it "off", because unless you take the battery out and discharge all capacitors it could still be recording and then upload the swag at the next available opportunity. I'm not saying it's actually doing this, but it "has the technology" and unless your phone has 100% free-as-in-liberty software that you compiled and installed yourself, there's no way to tell if it's doing this or not.
Here's a recent item from Forbes, not usually dismissed as a long-haired hippy tinfoil-hat publication: http://www.forbes.com/sites/adriankingsleyhughes/2012/10/03/how-your-android-smartphone-could-be-used-to-spy-on-you/
What are the engineering and design challenges in creating successful IoT devices? These devices are usually small, resource-constrained electronics designed to sense, collect, send, and/or interpret data. Some of the devices need to be smart enough to act upon data in real time, 24/7. Are the design challenges the same as with embedded systems, but with a little developer- and IT-skills added in? What do engineers need to know? Rick Merritt talks with two experts about the tools and best options for designing IoT devices in 2016. Specifically the guests will discuss sensors, security, and lessons from IoT deployments.