Some people get a 25% price reduction on house/renters insurance for having an active security system. Its worth asking. Also, a 95-cent Sliding Window Lock with Thumbscrews (2-Pack)-U 9802 - from The Home Depot is a cheap security measure!
Prime-Line Sliding Window Lock with Double Thumbscrews
The Defender Security Sliding Window Lock With Double Thumbscrews securely locks windows in a closed or ventilating position. The lock features 2 thumbscrews for additional gripping power....Learn More
Yale Sash Window Locks in a Pack of 6 At Door furniture direct we sell high quality products at great value including Packet of 6 Yale Sash Window Locks in our Window Security range. We also offer free delivery when you spend over GBP50. http://www.MightGet.com/january-2017-12/yale-sash-window-locks-in-a-pack-of-6.asp
On our first floor we installed 2 inch door latches on the window frame for security. Works as a window stop and no one can lift our windows higher than the latch. Yet we just retract it if we want to open the window all the way.
Keeping doors windows locked is 1st line of defense. Make wireless alarms your 2nd. The alarms are activated by doors or windows opening. Burglars hate noises, so even a small alarm usually sends them running. The alarms are available at home centers ($20-door alarms; $7-window). Or check out Intermatic at intermatic.com or Door Window Alarms at doorandwindowalams.com. Use alarms for doors windows in “hidden” areas of the house where you don't normally gather and that are often dark.