This could give patients vital time to take anti-inflammatory medicines and prevent a serious episode that may otherwise land them in hospital.
The Siemens device is the size of a mobile phone and works by analysing a patient's breath and measuring the amount of nitrogen monoxide (NO).
It is so sensitive it can measure amounts as small as one ppb (part per billion), which is the same as the dilution of a cube of sugar in a 50m swimming pool.
Heightened levels signals that an asthma sufferer’s air passages are about to become inflamed. This latent inflammation generally spreads hours before a patient becomes aware that anything is wrong.
The prototype device will allow patients to analyse their breath themselves and take the minimum amount of preventive medication when necessary.