Fall (Autumn) is an amazing time to be in the mountains. The colours are gorgeous, the temperatures are cooler and soft light makes for exceptional photography. However, the shoulder season is an incredibly dangerous time of year for tourists, inexperienced or over-confident hikers who are unprepared still with a summer hiking mindset and a limited understanding of the constantly changing conditions at higher altitudes.
Down in the city there can be sunshine with no sign of snow or ice, but a 1,000m higher or more the situation can be drastically different. While most of the trails may still be clear, there may be occasional snow drifts. What makes them really dangerous is the lack of continual snow fall, freezing overnight temps, and colder days turning these snow drifts into hard snow and slick ice.
If you are going out hiking in running shoes or hiking boots it is important to throw some trail crampons into your backpack. You might not need them, but there is no harm in having them available in case you come across a brief section of snow or ice. All it takes is one slip to break an arm or bang your head on a rock and you turn a great day into a life or death situation.
Also wear non cotton clothes that are layerable. You may still get hot hiking up and may only need a shirt and shorts/leggings, but once you reach a higher altitude the temperatures can be bitterly cold. Try to avoid sweating and wear fabrics that don't hold water. Always bring a warm coat. Its inconvenient to pack a lot of gear, but you shouldn't risk not doing so. You will need a good expandable running pack or backpack with a lot of space.
Even for day hikes it is crucial to bring two headlights. A backup is important in case your first light doesnt have a full charge or if you get really delayed and spend hours out. A battery pack is good too so you can plug in and charge your light and a mobile phone. Read up on the ten essentials to take with you as well. When in doubt about your safety or location always call emergency services who will advise you of the best course of action.