How can you know if your puffer is running low?

The most common way to figure out is to gently shake the bottle and the quantity would be figured out. The other method is the one, which is not recommended by the manufacturers of this asthma treatment. The method is to remove the plastic cap and put a drop of the aerosol into a bowl of water. The way the water floats can let you know if the puffer is running out. Neverthless it is always a good idea to have a spare puffer with you so that it is available all the time.