Even though Frenchies do not bark a lot and can sleep with the best of them, they are generally fairly decent watch dogs. Our Frenchies alert us to unexpected visits, like the UPS man, or some unexpected event. Frenchies can become somewhat territorial and protective, which are assets for a watch dog.
The funny thing is that they seem to sense very quickly when people come over for a visit that they know. When our sons and their family members or known neighbors show up, it doesn’t seem to put our Frenchies on alert at all, like it did our Yorkies who would bark like crazy until they finally figured out who the intruders were. It’s only when someone shows up that they have never seen before that they tend to get a little excited.
There are certainly better watch dog breeds if this is primarily what you are looking for, but if you are looking for a great companion first, that can also function as a watchdog, then the Frenchie is a great choice. You can count on your Frenchie letting you know when a stranger approaches or the house is on fire.