barb
barbed
barbwire
barrier
base
border
cell
cellular
closed
communication
construction
defend
defense
detail
door
entry
equipment
fence
forbidden
frame
framework
grid
guard
iron
lattice
line
mesh
metal
mobile
obstacle
pattern
private
protection
red
restricted
safety
secure
security
sharp
station
steel
structure
telecom
telecommunication
tower
transmitter
wall
wire