The other option is to build your own Siren/Strobe with ‘off the shelf’ components and use a SmartPower Outlet to turn it on and off. This is the set-up I have, probably cost me $75 total but its will blow any of these cheap sirens/strobes away!
Parts you will need:
Siren
You can find these for $10-$50 and in many different form factors depending on your needs. One is used was Honeywell Ademco 748 119db Dual-Tone Siren
Strobe (If you desire)
Prices on these are all over the place. Can find as cheap as $10 all the way to $150 (heavy duty outdoor models). Again many different for factors to choose from here, there are flush wall mount strobes (<1" thick) that are clear or there are plenty of other options. My suggestion would be to go with a cheap one as it will likely only be set-off a few times a year (hopefully by accident) and tested periodically, you do not need to buy strobes that are rated for 10-20years of continuous use.
Power Supply
As both the siren and strobe you buy will likely be 12-24VDC you will need one of these to power it. Simply cut connector from the end and hard wire to your strobe/siren. Just make sure whatever you power supply you buy has the correct VDC and amps to run both siren and strobe.
SmartPlug
Your DC power supply will plug into this (or other ST compatible plug) and then all the rules you build will turn on or off the SmartPlug to trigger the alarm.
What I love about this is the flexibility to build with components based on your needs. You can run no strobe or a big/small strobe. You can choose a loud or quiet Indoor Siren and add an outdoor siren if you want too.
When I get home I can take some pictures of my set-up if you would like.