According to safety and peace rankings, Portugal is considered one of the safest countries in the world. Bicycle thefts generally only occur in major urban areas. The Alentejo region, in particular, is quite peaceful. In four editions and after the participation of hundreds of riders, there has never been a single incident of bicycle or equipment theft at the Gravel Birds event.
However, this doesn't mean there can't be a first time. The event has gained significant visibility in Portugal. People with malicious intent will easily know that there's a cycling event with dozens of expensive bicycles and a tracking system indicating the participants' locations.
For this reason, it's never excessive to take preventative security measures. Answering directly the question: yes, we advise you to carry and use a lock, in Castro Verde (including at the entrance to the briefing and dinner locations) and along the route. Currently, there are several lightweight lock options available in the market. A lock won't work miracles against certain tools, but it will always play a preventative and deterrent role. Other security measures are advisable: always collect and carry key items such as wallets, phone, keys and GPS devices, and use your helmet as a lock as well (linking wheel and frame).