Under the EIO Directive : Luxembourg authorities comply with the formalities and procedures expressly indicated by the issuing authority unless such formalities and procedures are not contrary to the fundamental principles of Luxembourg Law. Besides the grounds of non-recognition/execution provided under art. 11 Directive 2014/41/EU, recognition and execution might be refused where the measure would be contrary to the fundamental principles of Luxemburg Law.
Under MLA instruments: To be requested by international letters rogatory. Contents: an indication of the authority making the request; a summary of the facts; confirmation that a lawful observation order or warrant has been issued in connection with a criminal investigation; precise information for the purpose of identifying the subject or object of the observation ; an indication of the criminal conduct under investigation; the desired duration of the observation; and where applicable, the provision of sufficient technical data to ensure that the request can be met. Execution of the measure in conformity with the procedure applicable in the requesting State : possible as a matter of principle; to be assessed on a case by case basis. Relevant formalities to be expressly indicated.
Irrespective the statutory basis, duration limited to one month; prolongation possible on a monthly basis as long as necessary, maximum length of one year. Outcome of the measure to be put down in a written report.