A bicycle wheel has a nominal radius, plus a tyre on the outside will give you a diameter. That will give you a circumference, something like 1500-2500 mm depending on the wheel rim size.
So set up a reflective patch between two adjacent spokes, and use an optical sensor to detect when that patch goes past. Simply have tuo tune the sensor so it doesn't see spokes, but does see the reflector. If that doesn't work, you could use a magnet and a magnetic pickup like a simple bike computer. Each pass is one wheel revolution.
Simply count the pulses and send your interrupt/trap/signal/message when you hit 72 pulses/wheel revolutions (assuming a tyre circumference of 2235mm)
There are 160,935 millimetres in 0.1 miles.