These days, you don't need to sit outside in a van with your headphones on, listening to static for an hour before the battery runs out and the tape recorder gives a tell-tale clunk.
Tiny matchbox-sized gadgets are now capable of transmitting audio and video for hours on end to the other side of the world.
Not only that, but we are all constantly connected to the internet via mobile phones and computers, and happily share details of our work and home life on social media - all valuable information for spies.
