Wylie, do you need to get 100% return on the investment to consider the improvement?
Have you asked your your current insurer whether you require window locks or only asked the new insurers?
One week's lost rent in not having a tenant willing to accept the risk of not having window locks would come close to the cost of installing them. Multiply this by several lost opportunities over the time that you own the premises.
I don't even think of the return generally. We just installed $2K of security grills to a house where robberies have happened in the surrounding streets. No rent increase at all.
We are this week adding a security door to a house for the benefit of the tenant to enjoy the breezes - no rent increase at all. Some investors would call us stupid, but we are just happy to do things to benefit a sitting tenant, but mindful that what we do increases the desirability of the house for the next tenant.
I am a bit offended actually if you are taking my posts to mean I won't do anything without having 100% return.
We did offer to build a back deck in exchange for extra rent, but the tenant had just moved in, was keen to stay for several years, and didn't want to pay any more, and we were not going to spend $20K (maybe up to $25K) with no increase to offset the cost of borrowing to do it and no prospect of being able to charge market rate for such an improvement for several years. Does that make me greedy? I don't think so.
But, honestly, we have just never, ever had any window lock issues in all the years I've been a landlord. Most of the IPs we look after have some security, enough that tenants can leave windows open all day and be safe, whilst closing (without keys) other windows like most houses in Brisbane do. I've been doing this for over 30 years and my parents had been landlords for longer, and it has never been asked. Perhaps it is a Queensland "thing". Same as some on here cannot imagine renting out a house without insect screens. We've never, ever been asked for them either.
And we don't have them on our own houses, and never have.
Believe me, if it was something stopping a tenant renting our house, we would be adding window locks.
P.S. Regarding insurers. In all the years I've been doing this, keyed window locks is a question I'm asked every single time. I've never had any trouble when I've said we don't have them. That is Commbank, QBE, Suncorp, Youi and more.