A telepath arguably has no choice. Thoughts after all are just biochemically generated electromagnetic pulses, and all telepathy is is just simply having a good enough aerial to pick up these transmissions. The genre is full of stories were telepaths have to erect shields or take chemical blockers or drink excessively not to protect your privacy, but to protect theirs from being ceaselessly spammed.
Accessing memories is more problematic, and could work either on the principle of RFID chips (which are inert and only send a signal back via a completely involuntary process when they are powered up by the energy contained by an incoming signal querying them) or a hard drive (which even in stand-by mode is powered and thus search activity is much more noticeable/deliberate)