Eavesdropping used to mean carrying around a purpose-built recording device. If someone spotted it, the jig was probably up! But with a smartphone audio recording app and gigabytes of storage, your phone could theoretically record everything within earshot all day long. Just make sure you know the law. I use Talk-a-Tape Audio Recorder to make sure I don't miss great quotes in interviews (but I ask people first).
Hidden CameraIf you want to covertly snap a photo or video, your smartphone's a fantastic tool... except many smartphone cameras make an obvious sound, and the extra-large viewfinders mean you won't be fooling others around you. Mobile Hidden Camera for Android is about as stealthy as it gets. The app lets you take pictures from a totally blank screen, or even inside a fully-functioning notepad app. And get this: if you type a designated kill word into the notepad app, it'll immediately erase all the photos and videos you've taken. We've also seen other hidden camera apps that can take pictures when you whistle, or when they detect motion.
Slow Motion Video
FLIR One / Seek Thermal
Ryobi Inspection Scope
GammaPix Radiation Detector
iPin Laser Pointer
Smartphone Spy Lens
Wickr Top Secret MessengerOnce you've got the intel, how do you safely send it back to base? Nothing's foolproof, butWickr's messaging app sure sounds like it's got the right features for amateur spying. Military-grade encryption, self-destructing messages, and an anti-screencap design means your sent snapshots will probably stay for-your-eyes-only.
source: gizmodo.com by Sean Hollister