Getting A UPS

[#1]

I've been thinking about this for a year or two.
It's not that our area is particularly prone to power cuts, it's just that -- when they do happen - they're a bit odd.
The power goes off, then after a few seconds comes back on again, then goes off again after a few more seconds, then back on again for a few more seconds and then goes off for about an hour.
This, I reasoned, is not going to do my PC any good at all, from the point of view of config/OS problems if nothing else.
It's mostly inertia which has stopped me from getting one so far, but as the season of winds and worse beckons, I thought it might be worth doing now.
A few questions I'd be grateful for answers/suggestions to:
1) Would a UPS protect me in the event of the sort of outage I've just described?
2) Would I need one only for the actual PC tower unit, or would I need to protect anything else - router, monitor, printer? I currently (ho, ho!) run them all through a surge protector in any case, but a combined SP & UPS would, I presume, cover all bases?
3) Can anyone recommend a small, reliable model or two for me to look into?
TIA

[#2]

Interesting that you posted this today as it was something I have been thinking about since another outage yesterday morning.
We have three or four a year. Occasionally they are as you describe. But with two PCs and various peripherals scattered around the house I'm concerned about the additional cost.

[#3]

It's worth putting your router on to a UPS which means that you can do an orderly disconnect.
I have had a APC Back-UPS 550ES for some considerable time - I've just had to replace the battery in it.

[#4]

APC are the only one's I have used (in a professional capacity) and have found them very reliable.

[#5]

As above - get a decent brand if you can afford it. APC are the best out there.
Get the highest VA rating you can afford  - it will last longer before running out of puff.
Only use it for the monitor and base unit. It will protect in the case of a powercut for anything from tenths of seconds to 10+ minutes depending on the load and the model - higher models can let more energy effiicent machines run for an hour or more. The idea is to protect your PC from brownouts (low voltage dropouts) and blackouts (power failures) from fractions of seconds to enough time to let you shutdown your machine after safely saving your data.
I've seen people only use it on the base unit then panic when they realise that their monitor has no power and they can't see what they are doing to save their data  
A lot of units will also switch over to the UPS in case of mains overvoltage too and will iron out nasty spikes.
Hope that helps

[#6]

The ones I used (can't recall the model number) had the facility to gracefully shut down your PC before the battery was exhausted.

[#7]

I have an APC UPS.  It does not protect my router from losing sync in the event of a power cut but it does allow the router to re-sync.  The computer keeps going without interruption.  The battery does not last long enough to keep the computer running in the event of an extended power cut.
I think the pattern of power failure you describe is the legacy of some protection system that does not work any more because of excess demand.  The first cut causes an automatic protection system to come on to try to restore the power but this finds it is overloaded so the power goes off again a few seconds later.  In your case it seems that a third level of protection is triggered which then fails in turn.

[#8]

Before I had to move my router downstairs (long story) I had it on the UPS and never lost sync on a power cut until I did a proper disconnect when I decided it wasn't coming back soon and shut everything down.
Having monitors on the UPS was a problem with CRT monitors, but modern monitors use less power.
Strat: Most (all?) APC models have the ability to initiate a shutdown if you install the software and connect the UPS with a serial or USB signal cable.

[#9]

Not all UPS's will have an interface to signal the PC to shut down.
Off the top of my head (I'm not 100% sure on this) there were UPS's with a simple RS232 interface which basically shorted a couple of wires to signal an "issue" (maybe CTS / DTR or something), smarter signalling used the RS232 port itself to signal data to the PC with information on the UPS status such as battery charge, runtime remaining and UPS load.
Newer UPS units have a USB interface which does a similar thing.
My APC SmartUps for the server has an RS232 port which uses three wires (I made my own cable) - RX/TX/GND and allows Linux to communicate with the UPS. It will shut down my server when there is 10 minutes or so of battery power left - I get around 45 minutes on a full charge. My UPS will also not come back online unless the power has been back on for a certain amount of time and the battery charge is above a certain level - this is pretty vital if you have say a 40 minute outage, power comes back on and then goes back off while the server is still booting but the batteries don't have enough charge to allow the server to finish booting then shut it down again.

[#10]

I've got something similiar to one of these (Scan keep changing the range of Liebert's they offer!) plugged in to my modem, router, downstairs switch and wireless AP.
I think I get about 5 minutes total with all of those running, much more if I shut down the PC based router.
That has, in the past, been enough time for someone to come along and swap out my electricity meter, although he did say the beeping (which increases in frequency as the battery depletes) made him feel like he was in Mission Impossible 
I don't use it to shutdown the Router-PC as I don't have a way to power it back on remotely (and unless the battery drains completely it won't respond to the Wake-on-AC signal). But that'll all change when I move from using the PC as a router to just a mail server when I finally finish configuring OpenWRT on the switch-wireless AP.

[#11]

Yeah a UPS would definitely help you judge, just be sure to get a good one and change the battery after a few years before it fails.
I had a second hand UPS given to me by a member of freecycle. It's done me a good 2 years but a week or so back the battery gave up and my system switched off when the missus unplugged it  For that reason spare batteries and a planned replacement schedule are a good idea.
As others have pointed out, remember to also power your monitor from it too (along with anything else that won't appreciate a sudden loss of power such as external HDDs). Routers don't really suffer any faults /. problems from power loss IMO though if like mine you have a usb HDD plugged into it then that could cause problems when the USB connection dies but the drive is still powered up.
Many UPS's have ketle lead type outputs on the back. Mine has 6 (and it's pretty basic compared to many) so you'll be ok for the monitor.

[#12]

Got myself an APC RS Pro 1200 230V Back UPS   . Expensive, but I found with the cheaper ones caused so much interference that the broadband crashed. This one - no problems. Electricity supply here is flaky; we have had several cuts > 2 hours in recent months. And we get the exact scenario mentioned by the OP - off/on/off/on/off/on/off.....
Attached are: Billion Bipac 7800n router, 1 x TP-link 8 port switch, 1 x Buffalo 4 drive Terastation NAS; 1 x Buffalo Drivestation, 1 x Buffalo Linkstation, 1 x Vodafone Suresignal. Also have 3 printers using surge protection only outlets
With all that lot running I get about an hour on battery, but if I power down gracefully all but the router I can keep going for nearly 4  hours (by which time my laptop battery will have run out anyway). The router doesn't  lose sync at all, even at the moment of mains power loss.

[#13]

I'd recommend putting the router on the UPS, if nothing else, it'll maintain internet access while the power is down, and you can still use mobiles, laptops, etc. without draining the UPS too quickly. 
On my setup the FTTC modem, router and DECT base station use 7%, and the UPS lasts around 1.5 hours,  with the PC and monitors on, it's around 40% and last for about 20 minutes.