If you (well, actually your dryer) experience any of the following (if you experience any of these please seek medical attention immediately):
Drying your clothes takes longer than  usual.
There is a burning smell coming from the dryer, when it’s on.
You notice lint stuck to the dryer or the wall next to the dryer.
Your laundry room or dryer area is excessively  warm and or moist.
Your vent flap  outside does not open and close properly (that’s the little thingy outside that hot air comes out of and flaps up and down.)
If there is a bird’s nest on the outside of your dryer vent exhaust (hint – you probably should have called us a while ago.)