Usually I do my F.O.H House-Keeping Announcement very formally spoken (Welcome Ladies and Gentlemen.... the fire exits... phones turned off)
This year i wan to add in humor and make people listen to the announcement more.
What should I Do
You mentioned fire exits, so I know you know that the announcement is an important safety and liability issue, but I'll nevertheless say that while humor can be great you have to walk a thin line there. I've had to order re-dos of pre-show announcements before because someone got too cute with the delivery and the audience either didn't take it seriously or didn't even understand it all. In most cases it isn't really supposed to be part of the show, so simple and professional is appropriate. Blue Man Group used to do a very funny one making fun of latecomers etc, but as I recall they also took care of the important business simply and professionally.