Trying to activate new sim card | Technical service details | Consumer forum

I purchased a wireless alarm system for my home, it will use the GSM frequency I can't seem to figure out how to activate the sim card. inserted into the main unit, so it can make calls/sms if there an intrusion... In order to activate the sim card I must have a 15 digit "IMEI" number, which my unit does not have, I tried interring the serial # but not enough digits... Any sugestions