  We describe a detector of alpha particles based on wire type counters
(single-wire and multiwire) operating in ambient air at high gas gains
(100-1000). The main advantages of these detectors are: low cost, robustness
and ability to operate in humid air. The minimum detectable activity achieved
with the multiwire detector for an integration time of 1 min is 140 Bq per m3,
which is comparable to that featured by commercial devices. Owing to such
features the detector is suited for massive application, for example for
continuous monitoring of Rn or Po contaminations or, as discussed in the paper,
its use in a network of Rn counters in areas affected by earth-quakes in order
to verify, on a solid statistical basis, the envisaged correlation between the
sudden Rn appearance and a forthcoming earthquake.
