Most of my expertise is relate to Exotic Shorthairs (shorthaired persians), but I think I can handle this one!
As far as sharing a crate goes, DEFINITELY NOT! The confined space and the mother's natural instinct to wean her baby (not just eating wise, but socially) could cause aggresion between the two. Furthermore, you want mommas milk supply to dry up and it won't if baby wants to still nurse. My kitty Flame had to be permanently seperated from our Lucy because we would find Lucy "snacking" on Flame all the way up to 4 months old. This was not a good thing because in my kitties that can lead to infection if the milk is not gradually decreased and eliminated. I'm not sure if this can happen in dogs, but ask your vet to be sure. Furthermore, you want to encourage independence in the puppy and give momma a chance to rest.
As far as the alarm goes, I agree with everyone else about the whining. A puppy will whine when it needs to go. However, if you're a heavy sleeper, you may wake up to a soggy puppy. Once a puppy has too many accidents (for some puppies it's once inside the crate) it can be impossible to fully housebreak after that.
Also, I would not carry the puppy outside when it needs to go potty. Let it walk so that it knows where it is going and how the potty routine is supposed to go. You may get an accident or two, but just be patient, stick the puppy's nose in the pee, tell it no gently, and put it outside where it is supoosed to go potty. If you get upset or use too strong of a tone you will have a puppy that pee pees whenever you discipline it, so be gentile. Also, give treats after every successful potty. The puppy will get the idea that outside pee pee means treat and inside potty means no treat and a yucky sniffer.
Petsmart has a video on crate training that is very helpful, and they also have a take home pamphlet. You may want to look into that and also talk to your vet about his/her feelings on crate training.
Good luck to you!
ps-chihuahas are very sensative to the tone of your voice (i'm sure you already know that) so the more praise you give the better!
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