An impact is detected with a vehicle having a body comprising parts which are deformable in an impact, by a secondary impact detection system configured to detect an impact that may not trigger a primary impact detection system. The secondary impact detection system comprises a plurality of deformation sensors attached to the deformable parts and configured to detect bending of the deformable parts. One or more processors are configured to receive a plurality of respective outputs from the plurality of deformation sensors, process the respective outputs to increase sensitivity to short-term changes relative to long-term changes and generate an indication of an impact dependent on detecting a processed output meeting a predetermined criterion. Outputs associated with a group of neighboring flex sensors may be used to localize the impact, characterize the source of impact, and/or reduce a likelihood of a false positive associated with the detection.