how can i get my 4yr to spot having accidents

I have a five yr old and a 4 yr old both boys. i had no problem with my oldest on potty training not even any accidents. he was trained by 2. but my 4yr old has been having some accidents at preschool, i dont know what to do. he doesnt have any accidents at home during the day just once in a while at school. but at night time while he is sleeping he has accidents so what is some advice to get him to recogize that he has to ggo pee before its to late. and it only him peeing not pooping in his pants

[musicmama]

Some children's bladder's develop slower than others.  Making a big deal over it might make him more anxious.  I would always have a back up outfit in his backpack just in case.  At bedtime, let him wear a pull up.  Some children take a while to outgrow this.  I'f he's in a pull up, he can still wake up clean and feel good about himself.  You might want to really brag every time he keeps his pull up clean or every time he doesn't have to use his back up outfit at school.  Good luck and God bless.