Plain version: a warranty is a statement or promise that is part of the policy itself and must be true or kept, such as "a night guard will be on duty" or "a central alarm is in service." A representation is something the applicant tells the insurer to get the policy; a warranty is written into the contract.
Types and form:
A warranty is either express or implied (§440).
A statement in a policy of a matter relating to the person or thing insured, or to the risk, as a fact, is an express warranty (§441).
No particular form of words is needed (§442).
A warranty may relate to the past, the present, the future, or any of these (§444).
Material vs. immaterial: §447 lets the insurer rescind for violation of a material warranty or other material provision. Under §448, unless the policy declares that violating specified provisions will avoid it, breach of an immaterial provision does not avoid the policy.
Breach without fraud (§449): it merely exonerates the insurer from the time the breach occurs, or, if the warranty is broken at its inception, prevents the policy from attaching to the risk. Example: a jeweler stops the guard service on March 1. A covered theft on February 10 stays covered, and if the insurer does not rescind, it is released only from March 1 forward.