Can police arrest without a warrant?

Yes, but only for cognizable offences, and they must follow proper procedure.

Police can arrest without warrant for cognizable offences (serious crimes like murder, robbery, etc.). For non-cognizable offences (minor offences), they need a warrant from a magistrate. In either case: (1) They must tell you why you are being arrested, (2) You can call a lawyer, (3) You must be produced before a magistrate within 24 hours, (4) Women cannot be arrested after sunset and before sunrise except by a female officer with magistrate's permission.

• BNSS Section 35 — When police may arrest without warrant
• BNSS Section 36 — Procedure of arrest
• BNSS Section 187 — Person to be produced before Magistrate within 24 hours
• Article 22 — Protection against arrest and detention