It depends on the voice assistant. Currently, Siri and Gemini for Home can dial 911 for you -- which is helpful if you're really short on time and your hands are shaky. In fact, Gemini has been known to get overeager and call 911 when instructed not to. Alexa cannot call 911, unless you pay for the Alexa Emergency Assist feature, which lets you call emergency services. (The feature will cost you $6 per month.)
Voice assistants like Alexa are good at tapping into information about protecting your home from fires, and are particularly knowledgeable about fire extinguishers. They readily supplied me with information not only on where to put them (kitchens and garages, where many fires start), but also how high to mount them on a wall and what not to do with an extinguisher (put it over the stovetop, for example).
This is a useful question when you're installing or upgrading any kinds of smoke detectors in your home, whether a single device or a DIY security system. I found certain voice assistants were better than others at this question. Gemini for Home was the most useful, tapping into a government site and giving specific information on exactly where the state required homes to install smoke alarms. In fact, Gemini's summary was so long first-time users might find all the info overwhelming, which is why it may be helpful to use a web search for a question like this. Siri gave some helpful info, but
If your voice assistant can connect to your home security system (both Alexa and Gemini for Home usually can), then you can ask them if your security system is armed or not. That's useful if you aren't at home and someone is making a surprise visit to your house, or if you are arming your system manually and can't remember if it's on or not.