ON most days of the month a woman cannot become pregnant. Persona - consisting of a hand-held monitor and disposable urine-test sticks - identifies those days by measuring a woman's hormone levels through a simple urine test. At 94 per cent, it has the same effectiveness rate as a condom.
On the first morning of a woman's period she presses a button on the Persona monitor. Each morning she checks which light - green, yellow or red - is displayed on the monitor.
A green light means she is free to have sex without a contraceptive. On red light days she is at risk of getting pregnant and she should avoid having sex or she may choose to use another form of contraception.
On eight mornings of every cycle a yellow light will appear, which means she needs to do a urine test to tell if it is safe to have sex.
After the first few months, Persona will typically identify 6 to 10 red light days each cycle. A starter pack costs £49.99. A month's supply of test sticks is £9.99. It is available in pharmacies.