The South Korean military had touted its highly sophisticated security system installed along the inter-Korean border that used to be patrolled by soldiers on foot.
Thermal observation devices, CCTV cameras and optical units are installed along the barbed-wire fence that lines the heavily fortified inter-Korean border to detect movement and the presence of humans.
When pressure is applied to one of its sensors, an alert goes out so that soldiers can inspect the area manually.
But when a North Korean man crossed over the fence earlier this month, the fence's alarms were not set off.
This prompted the South Korean military to launch a probe into its security system.
An official at Seoul's Joint Chiefs of Staff said the man had somehow been able to use one of the fence's steel pillars to maintain his balance and in the process the sensors did not pick up a major shift in weight.
There's also the possibility that the man had put pressure on the sensors but the alarm was not set off due to a malfunction.
A South Korean military official said that rather than having faulty parts, the malfunction could be due to the sensor's deterioration after being exposed to high winds and bad weather for more than five years.
The military says it plans to conduct a full inspection of all of its detectors along the border and install improved versions as well as improve maintenance training in order to get rid of any blind spots in border security.
Kim Ji-yeon, Arirang News.