There are 2 ways of looking @ alarms, do you want features or "fit and forget" functionality? This is what I always used to ask customers when fitting alarms for them.

If they want "fit and forget", then a Toad ai606 every day of the week. IT has less wires to run than a ai101CL, has more options and simply works. I have an ai606 installed on 3 of my vehicles (I have 8 in the family) and they have not gone wrong yet.

If they want features, then a Clifford is more likely. The problems with Cliffords almost always boil down to the installer (I only know of 4 fitters I would ever trust to go near a car or recommend, and 2 of them have now retired). If fitted quickly or poorly, they WILL go wrong or be tempremental. Period. The rest of the time, they go wrong because of user error and not reading the manual, for example, putting the alarm into valet mode before disconnecting the battery or jumpstarting from another source, otherwise the alarm can tend to "freak" itself out due to the voltage "spike" when power comes back.

As for power drains, the most draining part of most modern alarm systems is the LED that is on display. On Cliffords, if left armed for over 48 hours continuous, the LED flashes @ a reduced rate precisely to avoid an excessive parasitic drain.

Most alarms now only power up the internal relays and circuitry when the alarm is disarmed and the ignition is on. I have a top of the range Clifford on one of my vehicles, with ALL the extra options (totalling well over £1000 if I had it fitted @ retail prices) including multiple sirens, battery backup and normal, and it drains the battery as quick as another, almost identical car I have which has a more basic Clifford with not even half the accessories. I have left both cars for over a month without going near them and they have started with no bother. The Toad I have drains in roughly the same amount of time as the Cliffords.

As for the sirens "knowing when the car is running", most modern ones have an "ignition sense" wire which activates the charging facility only when the ignition is turned on (sensed via the main alarm unit), preventing a drain when armed. If the siren is draining, chances are it is an externally powered one (only takes a single feed from the alarm module purely to activate the siren) and normally has a key access to override if the battery is disconnected or the alarm has not been installed correctly and a "false" ignition feed is being sensed. Batteries can, and do fail internally in sirens, a battery can only be charged for so many cycles before degredation occurs. Again, modern technology can, and does, help slow this process down.

One thing to remember with Clifford is that they were taken over a few years ago by Directed Electronics (who make Avital, Viper, Hornet, etc...) and the quality DID go down a little. I think they may even have been sold again recently. The best Cliffords of recent times were the G3, G4 and 1st edition G5 series IMO. (Examples, G5 Concept 750 is 1st edition, G5 Concept 770 is 2nd edition). The later G5 are not as good as they have gone overly complicated to install, meaning more things to potentially go wrong.