It depends on why the helmet broke. If it's a manufacturer's defect, Smith Optics helmets are covered for three years from the date of purchase.
If your helmet was in a crash, stop using it immediately. Smith Optics offers 40% off MSRP on a replacement through its crash replacement program. To qualify, the crash must be activity-related, reported within two years of purchase with proof of purchase, and you'll need to present the damaged helmet along with details of the incident. The program is limited to one replacement per year, applies only to the original owner, and excludes helmet abuse.