Say nothing that you will not want played back. Leave no messages. Stay off the computer. Your hard disk will always rat on you. Watch it with gifts, or pay cash.
Credit cards leave a trail.
Don't use electronic zappers to pay bridge or tunnel tolls. As for Nixon's bugging system, five microphones were installed in the president's White House desk, implanted under the wood trim, and two more were placed on lighting fixtures across the room. These systems were voice-activated. Sound from the Oval Office was fed to two Sony 800Bs in a small White House room. The two Oval Office recorders were controlled by a timer.