Well, the answer to that is...cute!
Known as a Chorkie, the Chihuahua and Yorkshire Terrier cross is a gorgeous ball of fur, especially considering the two breeds it comes from are wonderful dogs in their own right.
Chorkies are high energy dogs (like their parents!) but they are very intelligent and can easily be trained.
Obviously being a small dog they won't be able to overpower an intruder but they will certainly bark to warn you that someone is around.Life expectancy of a Chorkie is 10-15 years and they tend to be healthier than their parents as they don't suffer with the common ailments of pure bred dogs.
Chorkies are light shedders and their ears should be checked regularly for excessive hair growth that can cause ear infections. They should be brushed and detangled daily with a bath every week or every other week.