Are these already good clients of yours? If so, then T&M. If it is someone that called you up and is "shopping around", it is probably not worth the time or effort to try and "win" the job with a lower quote. I would probably have at least 6 hours at our normal hourly rate in an estimate (estimate being the key word) for that job. Maybe more if you are not familiar with the product or the configuration. Not to mention what if they have crappy wi-fi? What if one of the smokes is at the top of a 24' vaulted ceiling and you have to rent a giant ladder to get to it? Those are all things that you would already know if this is a client you have worked with before obviously. Which comes back to my original statement of billing for T&M. I do not think any of our "regulars" would argue with me on that. YMMV.