This has been discussed in a few threads prior.
"In order to avoid damage to non-PoE devices, a key component of the 802.3af PoE standard is detection. PSEs must be able to detect the presence of a PoE-enabled device before sending power, and must be able to detect when the powered device is no longer present and remove power. To achieve accurate detection, a low-level detection current is sent from the PSE through the cable and the response is analyzed to determine if a compliant device is attached."
The majority of all corporate environments operate with POE switches and hardware because of the mass deployment of IP phones. However, you may still connect devices like dumb switches, desktops, laptops, etc to this same outlets without issue.