Thanks for the replies everyone!

The actual intent of the thermostat is to benefit my grandfather's
health. They have central air conditioning and he does not understand
that if he turns the system off, it takes all day to cool the house
again. He is suffering from a few health problems that go along with
his age (90), and we would like to keep the house climate as controlled
as possible since the heat definitely causes him problems.

I've searched a little more and will be checking the link or 2 posted
above. I've seen a few secure thermostats that range from about ~$80
to ~$300 so without a little more research, I'm not sure what we'll
decide on just yet.

P.S. it's not a *drastic* problem, it's just that when he messes with
the thermostat letting the house get up to 90, he's more or less
jeopardizing his health.