警犬的英文是 "police dog"。来源是因为警犬主要用于警方工作，所以称为 "police dog"。一些英文例句如下：

The police dog sniffed the suspect's belongings for drugs.

The police dog tracked the thief's scent and led the officers to his hiding place.

The police dog barked fiercely at the intruder, scaring him away.