Come on ADT!
For the last two nights our alarm has been going off. Last night, Thursday night, I noticed one of the beams had a flat battery. I requested that technical services come out on Friday to replace all batteries. Late Friday afternoon I contacted ADT and was told they could only come on Monday but at a fee of over R500 they could come out on Saturday. I decided to remove the beam temporarily and put it in an unused room.
I am writing this review at 01h15 because this same beam has continued to set the alarm off. A very nice gentleman has just called me to explain why they charge more over weekends, that the standby technician may not even have a spare battery and that the fact that the battery is flat causes the beam to set off the alarm. 
I had in the meantime disabled this beam by disconnecting the wire to the battery.
My question to ADT is this: Surely these batteries have a certain lifespan and customers should be informed that they need replacing by ADT technical staff? The beams here were all installed at the same time so it is only common sense that the other beams are also soon going to have flat batteries.
Come on ADT!
My thanks to the guards who were here quickly and were very kind and helpful.