Physical Danger
As with any job where your tiny fleshy fingers work with sharp, moving pieces of metal, you're going to want to be a wee bit careful. To start with, you shape keys, which are typically made out of brass and nickel instead of pillows and clouds. These materials require tools that will reshape you, too, if you aren't careful. Metal shavings can go a-flying, so wear safety glasses to protect your peepers as well. Power tools are, well, powerful.
Then, there's everything else you do in your daily life opening doors for other people. You'll have to replace and repair locks, and you may have to do it in places like rooftops or city sewers. You may get called to work on active construction sites, and that comes with a whole host of bodily-harm risks.
Oh, and did we mention the bodily harm inflicted upon you by others? It's rare, but you're going to people's houses to unlock doors; occasionally, the reasons behind a customer's call won't be all sunshine and lollipops. Estranged spouses may want you to let them into a house that no longer belongs to them, thieves may try to convince you a car is theirs when it totally isn't―you may even be called to the scene of a crime to unlock doors to CSI-type shenanigans.
By and large, though, you'll have very non-lethal days at the (mobile) office. We just think it's a good idea to remain aware and careful, because you really never know what lurks behind closed doors.