725 ILCS 5/108A-4: Grounds for Approval or Authorization.

The judge may authorize or approve the use of the eavesdropping device where it is found that:

(a) one party to the conversation has or will have consented to the use of the device;

(b) there is reasonable cause for believing that an individual is committing, has committed, or is about to commit a felony under Illinois law;

(c) there is reasonable cause for believing that particular conversations concerning that felony offense will be obtained through such use; and

(d) for any extension authorized, that further use of a device is warranted on similar grounds.