SPYON

Keep under surveillance

• Bug

• Follow

• Investigate, perhaps

• MONITOR?

• Observe covertly

• Observe furtively

• Observe secretly

• Observe surreptitiously

• Observe through a keyhole

• Secretly observe

• Secretly watch

• Snoop like Smiley

• Surveil

• Tail, maybe

• View slyly

• Watch

• Watch covertly

• Watch from hiding

• Watch from the trees, say

• Watch furtively

• Watch in secret

• Watch secretly

• Watch secretly: 2 wds.

• Watch slyly

• Watch surreptitiously

• Watch through a keyhole

• Watch through binoculars, say

• Watch, secret agent-style