Cash machines offer an ever-growing menu of services beyond merely dispensing money. For tampering criminals, this now includes a squirt of pepper spray in the face .

The extreme measure is the latest in South Africa's escalating war against armed robbers who target banks and cash delivery vans. The number of cash machines blown up with explosives has risen from 54 in 2006 to 387 in 2007 and nearly 500 last year.

The technology uses cameras to detect people tampering with the card slots. Another machine then ejects pepper spray to stun the culprit while police response teams race to the scene.

But the mechanism backfired in one incident last week when pepper spray was inadvertently inhaled by three technicians who required treatment from paramedics.

Patrick Wadula, spokesman for the Absa bank, which is piloting the scheme, told the Mail & Guardian Online: "During a routine maintenance check at an Absa ATM in Fish Hoek, the pepper spray device was accidentally activated.

"At the time there were no customers using the ATM. However, the spray spread into the shopping centre where the ATMs are situated."

In conjunction with the police, Absa is using the technology at 11 sites, identified as high-risk by branch managers.

If successful, it will be expanded to cash machines around the country.

Transporting money is one of South Africa's most risky occupations. In May a Group 4 security guard was killed in Johannesburg when a gang used explosives to blow open a cash transit van. His partner was shot in the back as he tried to escape.