Can I have the same alarm-tone for both exchange lines?

A modular jack is provided for each exchange line. You cannot parallel exchange lines into the same modular jack. Each jack has it's own set of four alarm-tones (and there is a different set of four tones for each jack). Each exchange line will therefore have it's own unique alarm tone. If you need to have the same alarm-tone for every line,  just purchase multiple Universal Alarms, connect each line to the same modular jack in each unit and program the same alarm-tone for each jack.