reconnoitre
be vigilant
be watchful
bug
case
course
cover
do
examine
eye
eyeball
follow
gaze at
go over
have a looksee
hold in view
keep in sight
keep in view
keep under observation
look after
look at
look on
look upon
make a reconnaissance
measure
observe
overpass
pass over
pass through
patrol
peep
perambulate
peregrinate
pererrate
play the spy
ply
probe
put under surveillance
range
range over
recognize
regard
scour
scour the country
scout
scout out
spy
spy out
spy upon
stake out
reconnoiters
recce
recon
reconnaissance
Reuter
goiter
loiter
reutter