You may hear it, though not recognize it. It can be pinking, crackling, a rattle... A Knock Link is the most convenient warning you can have without having a knock reading incorporated into something (like a PFC). You can get an A/F meter, but these need to have a wideband lambda sensor plumbed into the exhaust. Using the standard lambda achieves nothing. The meter will only give an A/F reading though. It won't tell you if det is actually occurring. The best method is to have a a set of det headphones which are used to listen to sound at the block. Jez uses these for mapping. Not very practical for everyday driving though...
Take my word for it though. If you are running the standard JDM map, which is setup with more advanced ignition and fuelling for 101 RON fuel, running 97/98 RON and high boost won't go. The JDM map is leaned off mid range. This is where det will occur.
When I got my Emanage mapped on the S15 for the first time by Jez, he confirmed that det was occurring at 0.8/0.9 bar on the standard map and running Optimax.