ADJ. unwanted, unwelcome | masked
VERB + INTRUDER catch, disturb, find, startle, surprise He surprised a masked intruder in the kitchen. | deter, keep away/out Dogs can deter unwelcome intruders. | tackle He was stabbed when he tackled an intruder armed with a knife. | repel Staff were instructed to repel intruders with physical force, if need be.
INTRUDER + VERB break into, force their way into Intruders had forced their way into the house.
INTRUDER + NOUN alarm
PREP. against ~s security measures against intruders