選択的
alarm
alert
alertness
cable
camcorder
camera
cctv
control
day
detection
deterrent
digital
electronic
guard
instrument
lens
modern
monitoring
nobody
observation
observe
outdoors
pole
precaution
privacy
private
property
protect
protection
record
resolution
safe
safety
secrecy
secure
security
sky
spy
spying
street
surveillance
survey
system
technology
television
tree
tv
video
watching