gps-trace.com service allows to add up to 5 units per account.
Only 1 "Vehicle" type and 4 "Personal" type tracking devices can be added per account.
Vehicle devices are added by clicking the "+" button in the lower right corner and personal devices by clicking on the "+" button in the lower left corner:
You can check your tracking device type in the list of supported devices:
If you need more unit then choose between following options:
1. create another account and add another 5 units and so on;
2. use commercial version.
!any off topic would be deleted!