Re-Use Telephone Wiring?

I bought a house with an old alarm wired up that I'm now replacing with an Elk.
 
The old system was wired exclusively with 6 conductor 24ga telephone wire by the look of it, and the only bit I want to re-use (as re-cabling to this location would be a nightmare) (and I'm doing Elk wireless everywhere else) is the outdoor speaker and strobe.
 
There are two wires running to the existing siren and strobe, one to each, and the wires have been tied together at either end to presumably allow more current to be carried.
 
My question is, can I re-use this or am I just asking for trouble? (I know that's perhaps a dumb question... but I'd appreciate experienced views here, this is not an install I'm doing for a customer, this is my own house and the speaker/strobe are just visual/auditory, the cellular dialer is summoning the good guys I hope).
 
My hope is to use 4 of the 6 conductors in wire 1 for the Elk outdoor speaker, and the other two for the tamper. And use all 6 wires in wire 2 for the Elk strobe.
 
Thanks.

My question is, can I re-use this or am I just asking for trouble?

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Personally here have reused 6 conductor solid core telephone cable (thinking though it was thicker than 24 guage wire) for my personal home alarm panel in the late 1980's. 
 
The 6 conductor non daisy chained telephone single run cable was old and did have a telephone transformer attached to it.  I removed the transformer / tested the conductivity with a VOM and used it for many years. 
 
The old panel had TTS / X10 and I used a pair of the wires for a speaker by the detached garage.  The old sirens and strobes were power suckers.  New piezo sirens and strobes are not these days.

I use this telephone wire for Ethernet. You only need 4 conductors for that and it works great. Sure, you won't get the fastest speeds, but it is good enough. The old wire is fine as long as you don't expect too much from it. Tie 2 or 3 wires together for higher currents.

grtaylor said:

The old system was wired exclusively with 6 conductor 24ga telephone wire by the look of it, and the only bit I want to re-use (as re-cabling to this location would be a nightmare) (and I'm doing Elk wireless everywhere else) is the outdoor speaker and strobe.

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Two 24 gauge conductors are roughly equivalent to a single 22 gauge conductor.  That might be ok to handle the current that the strobe requires, assuming it is the Elk strobe which requires about 210 mA or so and your wire length isn't too long (say less than 100 feet).  But it's a little skimpy for the speaker.
 
If you use 3 pairs for the speaker, 2 pairs for the strobe and 1 pair for the tamper, you'll be closer to where I think you need to be.
 
I'm never a fan of using multiple pairs of wire to increase current capacity, but sometimes you don't have much choice.
 
If I were wiring it from scratch, I would use 18 gauge for the strobe and 16 gauge for the speaker.  Maybe a bit of overkill, depending on the wire length.

Thanks for the feedback guys. I was expecting a barrage of 'rip open the walls and the attic and run the cable you cheapskate' so that's good news
 
I wasn't sure what current the speaker would pull, and yes both the strobe and the outdoor speaker are the Elk units. ELK-1RT and ELK-SL1.
 
What does the speaker pull when in full draw then? Not sure I have that accounted for in my load xls. And they haven't added a line for it which seems a little odd.

grtaylor said:

What does the speaker pull when in full draw then? Not sure I have that accounted for in my load xls. And they haven't added a line for it which seems a little odd.

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I've never tried to measure the power output of the M1 to a speaker connected to OUT2.  When using OUT2 for a siren, it is power limited to 1A, so I'll guess that also limits what it can deliver to a speaker.
 
You don't need to take the power for driving the speaker into consideration for the spreadsheet power calculations.  The M1 has a 2.5A power supply, of which 1A is reserved for powering devices connected to the M1's data bus and AUX power outputs.  That's what the spreadsheet is mainly concerned with. The remaining capacity of the power supply is available to power the M1 and speakers/sirens when it is in alarm mode.

Ah, that makes sense. Thanks RAL.