bugging
cloak-and-dagger work
counterespionage
counterintelligence
detection
electronic surveillance
espial
espionage
following
intelligence
intelligence work
looking
lookout
military intelligence
note
notice
observance
observation
regard
respect
secret police
secret service
shadowing
stakeout
surveillance
tailing
trailing
viewing
watch
watching
wiretap
wiretapping
witnessing
discovery
find
uncovering
vigil
allying
applying
belying
buying
complying
crying
decrying
defying
denying
drying
dyeing
dying
eyeing
flying
frying
implying
indemnifying
lying
misapplying
overflying
overlying
plying
prying
relying
replying
retrying
shying
sighing
supplying
tieing
trying
tying
underlying
undying
vying