Why has the output signal cadence changed?

In mid 2006 the unit's programming was altered to make the alarm more compliant with the simulated exchange-ring produced by PABX systems. The Universal Alarm will now work reliably when connected across an analogue ports of most PABX systems. The new program produces a broken output-signal cadence (i.e. if you hold down one of the test buttons and get a continuous output tone, then your unit has original programming. If the output tone is broken into bursts then your unit has the new programming.