I am about to move into a new house (rental) and was thinking to get a couple of battery-powered smoke detectors from Lazada. (as the house doesn't have any)

Is this a good idea? how much should I spend for a decent one? 
what about CO detectors, also needed? 

A fire consists of oxygen, fuel and heat. When considering fire protection you need to assess ignition sources as in powered appliances and power outlets and connections as well as likely combustible materials. A smoke detector assists where limited oxygen is present, such as a closed room. Well ventilated areas, sure smoke will occur, but fire blankets in the kitchen with areas considered a risk, such as storage of flammable liquids or proximity to living areas, even bedrooms, a water or similar if available alternative fire extinguishers, small or large, remembering they need regular servicing. Maybe yearly or replace. Nothing bar a water sprinkling system will fully protect, but every step is being prepared, than ignorance.

10 hours ago, triplez said:

I am about to move into a new house (rental) and was thinking to get a couple of battery-powered smoke detectors from Lazada. (as the house doesn't have any)

Is this a good idea? how much should I spend for a decent one? 

There are battery powered units available nowadays with a "10 year " battery.

Most will have bluetooth connectivity so if one alarms, they all alarm.

Indicators will show which area was the origin signal.

No requirement to replace internal batteries every 12 months as with many mains powered units.

In Aus, which is rather demanding place for any electrical installations, the approved units are now acceptable.

Cost would be around 2400 baht each.

Naturally there would be cheaper, unapproved units but you get what you pay for.

Thank you very much for the useful advice.