Bicycle-mounted crash avoidance technologies have been developed to improve cyclist safety. However, their effectiveness in alerting cyclists of potential dangers and the preferences of cyclists regarding the types and mechanisms of receiving alerts have not been examined extensively in field trials. To address this gap, this paper aims to understand how safety alerts are best communicated to cyclists. This aim was achieved by undertaking a field trial of a smartphone app, which was the user interface of an innovative Intersection Safety Alert System (ISAS). A total of 38 participants rode bicycles equipped with the ISAS in a 2-day field trial in downtown Melbourne, Australia, and then completed a technology acceptance survey. The survey data were analysed using statistical and thematic analysis methods to derive insights on how cycling safety technologies should be designed to ensure a good level of user acceptance. Results showed that cyclists would be willing to use or recommend a safety app that is free from privacy or security concerns, be able to provide alerts that can effectively notify about dangerous situations, and be effective in improving the safety for the whole cycling community. Cyclists preferred to receive simple and clear safety alerts that provided information on high-risk locations and the nature of dangers through an easy-to-use user interface that runs in the background and communicates with other cycling and navigational apps. They wanted the alerts to convey real-time and non-obvious traffic conditions and unpredictable movements of other road users. Preferences and comments regarding auditory, visual and haptic modalities of presenting alerts differed among riders.